Hello, Android 2nd Edition

everdin

贡献于2011-09-07

字数:400529 关键词: Android开发 移动开发 Clojure C/C++ Basic

What readers are saying about Hello, Android This is a most excellent book: very well written, easy to read, and fun. In addition, any of Android’s quirks are explained along with just the right amount of detail to ensure quality programming principles are followed. Anthony Stevens Founder and CTO, PocketJourney and Top 20 Winner of Google Android Competition Ed Burnette covers an impressive amount of ground in a nicely com- pact book while retaining the popular Pragmatic style. For the mate- rial on 2D and 3D graphics alone, this is worthy of a spot in any Android developer’s library. Mark Murphy Founder, CommonsWare I remember when I first started to work with Android; it was like a huge maze. With this book, the introduction would have been much less painful. I am convinced that by reading this book new Android programmers will have an easier start. Gabor Paller Senior Software Architect, OnRelay, Ltd. Prepared exclusively for Robert Walsh Download at WoweBook.Com Hello, Android Introducing Google’s Mobile Development Platform, 2nd Edition Ed Burnette The Pragmatic Bookshelf Raleigh, North Carolina Dallas, Texas Prepared exclusively for Robert Walsh Download at WoweBook.Com Many of the designations used by manufacturers and sellers to distinguish their prod- ucts are claimed as trademarks. Where those designations appear in this book, and The Pragmatic Programmers, LLC was aware of a trademark claim, the designations have been printed in initial capital letters or in all capitals. The Pragmatic Starter Kit, The Pragmatic Programmer, Pragmatic Programming, Pragmatic Bookshelf and the linking g device are trademarks of The Pragmatic Programmers, LLC. Portions of the book’s cover are reproduced from work created and shared by Google and used according to terms described in the Creative Commons 2.5 Attribution License. See http://code.google.com/policies.html#restrictions for details. Every precaution was taken in the preparation of this book. However, the publisher assumes no responsibility for errors or omissions, or for damages that may result from the use of information (including program listings) contained herein. Our Pragmatic courses, workshops, and other products can help you and your team create better software and have more fun. For more information, as well as the latest Pragmatic titles, please visit us at http://www.pragprog.com Copyright © 2009 Ed Burnette. All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmit- ted, in any form, or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior consent of the publisher. Printed in the United States of America. ISBN-10: 1-934356-49-2 ISBN-13: 978-1-934356-49-4 Printed on acid-free paper. P1.0 printing, October 2009 Version: 2009-10-6 Prepared exclusively for Robert Walsh Download at WoweBook.Com Contents Acknowledgments 9 Preface 10 What Makes Android Special? .................. 10 Who Should Read This Book? ................... 11 What’s in This Book? ........................ 12 What’s New for Cupcake? ..................... 12 What’s New for Donut? ....................... 13 Online Resources .......................... 13 Fast-Forward >> .......................... 14 I Introducing Android 15 1 Quick Start 16 1.1 Installing the Tools ..................... 16 1.2 Creating Your First Program ................ 20 1.3 Running on the Emulator ................. 20 1.4 Running on a Real Phone ................. 23 1.5 Fast-Forward >> ....................... 24 2 Key Concepts 27 2.1 The Big Picture ....................... 27 2.2 It’s Alive! ........................... 32 2.3 Building Blocks ....................... 36 2.4 Using Resources ...................... 37 2.5 Safe and Secure ....................... 38 2.6 Fast-Forward >> ....................... 39 Prepared exclusively for Robert Walsh Download at WoweBook.Com CONTENTS 6 II Android Basics 40 3 Designing the User Interface 41 3.1 Introducing the Sudoku Example ............. 41 3.2 Designing by Declaration ................. 42 3.3 Creating the Opening Screen ............... 43 3.4 Using Alternate Resources ................. 51 3.5 Implementing an About Box ................ 54 3.6 Applying a Theme ...................... 59 3.7 Adding a Menu ....................... 60 3.8 Adding Settings ....................... 63 3.9 Starting a New Game .................... 65 3.10 Debugging with Log Messages ............... 67 3.11 Debugging with the Debugger ............... 68 3.12 Exiting the Game ...................... 68 3.13 Fast-Forward >> ....................... 69 4 Exploring 2D Graphics 70 4.1 Learning the Basics ..................... 70 4.2 Adding Graphics to Sudoku ................ 75 4.3 Handling Input ....................... 84 4.4 The Rest of the Story .................... 90 4.5 Making More Improvements ................ 99 4.6 Fast-Forward >> ....................... 100 5 Multimedia 101 5.1 Playing Audio ........................ 101 5.2 Playing Video ........................ 107 5.3 Adding Sounds to Sudoku ................. 112 5.4 Fast-Forward >> ....................... 115 6 Storing Local Data 116 6.1 Adding Options to Sudoku ................. 116 6.2 Continuing an Old Game ................. 118 6.3 Remembering the Current Position ............ 120 6.4 Accessing the Internal File System ............ 122 6.5 Accessing SD Cards .................... 123 6.6 Fast-Forward >> ....................... 124 Report erratum this copy is (P1.0 printing, October 2009)Prepared exclusively for Robert Walsh Download at WoweBook.Com CONTENTS 7 III Beyond the Basics 125 7 The Connected World 126 7.1 Browsing by Intent ..................... 127 7.2 Web with a View ....................... 131 7.3 From JavaScript to Java and Back ............ 136 7.4 Using Web Services ..................... 143 7.5 Fast-Forward >> ....................... 154 8 Locating and Sensing 155 8.1 Location, Location, Location ................ 155 8.2 Set Sensors to Maximum ................. 161 8.3 Bird’s-Eye View ....................... 164 8.4 Fast-Forward >> ....................... 170 9 Putting SQL to Work 171 9.1 Introducing SQLite ..................... 171 9.2 SQL 101 ........................... 172 9.3 Hello, Database ....................... 174 9.4 Data Binding ......................... 182 9.5 Using a ContentProvider .................. 185 9.6 Implementing a ContentProvider ............. 188 9.7 Fast-Forward >> ....................... 189 10 3D Graphics in OpenGL 191 10.1 Understanding 3D Graphics ................ 191 10.2 Introducing OpenGL .................... 192 10.3 Building an OpenGL Program ............... 193 10.4 Rendering the Scene .................... 195 10.5 Building a Model ...................... 199 10.6 Lights, Camera, ... ..................... 202 10.7 Action! ............................ 205 10.8 Applying Texture ...................... 205 10.9 Peekaboo ........................... 209 10.10 Measuring Smoothness .................. 210 10.11 Fast-Forward >> ....................... 211 Report erratum this copy is (P1.0 printing, October 2009)Prepared exclusively for Robert Walsh Download at WoweBook.Com CONTENTS 8 IV Appendixes 212 A Java vs. the Android Language and APIs 213 A.1 Language Subset ...................... 213 A.2 Standard Library Subset .................. 215 A.3 Third-Party Libraries .................... 216 B Hello, Widget 217 B.1 Creating Your First Widget ................. 217 B.2 Calling All Widgets! ..................... 219 B.3 Stretchto Fit ......................... 220 B.4 The Rest of the Story .................... 221 B.5 Running the Widget ..................... 222 B.6 Keeping Up to Date ..................... 224 B.7 Go Wild ............................ 226 C Publishing to the Android Market 227 C.1 Preparing ........................... 227 C.2 Signing ............................ 230 C.3 Publishing .......................... 231 C.4 Updating ........................... 233 C.5 Closing thoughts ...................... 233 D Bibliography 235 Index 236 Report erratum this copy is (P1.0 printing, October 2009)Prepared exclusively for Robert Walsh Download at WoweBook.Com Acknowledgments I’d like to thank the many people who made this book possible, includ- ing my reviewers Anthony Stevens, Gabor Paller, Fred Burke, Dianne Hackborn, and Laurent Pontier for their attention to detail; Al Sutton for creating an early Donut SDK for developers; my editor Susannah Pfalzer for her great suggestions and good cheer in the face of impossi- ble deadlines; and especially my family for their patience in putting up with all the long hours. Prepared exclusively for Robert Walsh Download at WoweBook.Com Preface Android is a new open source software toolkit for mobile phones that was created by Google and the Open Handset Alliance. In a few years, it’s expected to be found in millions of cell phones and other mobile devices, making Android a major platform for application developers. Whether you’re a hobbyist or a professional programmer, whether you are doing it for fun or for profit, it’s time to learn more about developing for Android. This book will help you get started. What Makes Android Special? There are already many mobile platforms on the market today, includ- ing Symbian, iPhone, Windows Mobile, BlackBerry, Java Mobile Edi- tion, Linux Mobile (LiMo), and more. When I tell people about Android, their first question is often, Why do we need another mobile standard? Where’s the “wow”? Although some of its features have appeared before, Android is the first environment that combines the following: • A truly open, free development platform based on Linux and open source: Handset makers like it because they can use and cus- tomize the platform without paying a royalty. Developers like it because they know that the platform “has legs” and is not locked into any one vendor that may go under or be acquired. • A component-based architecture inspired by Internet mashups: Parts of one application can be used in another in ways not orig- inally envisioned by the developer. You can even replace built-in components with your own improved versions. This will unleash a new round of creativity in the mobile space. • Tons of built-in services out of the box: Location-based services use GPS or cell tower triangulation to let you customize the user expe- rience depending on where you are. A full-powered SQL database Prepared exclusively for Robert Walsh Download at WoweBook.Com WHO SHOULD READ THIS BOOK? 11 lets you harness the power of local storage for occasionally con- nected computing and synchronization. Browser and map views can be embedded directly in your applications. All these built-in capabilities help raise the bar on functionality while lowering your development costs. • Automatic management of the application life cycle: Programs are isolated from each other by multiple layers of security, which will provide a level of system stability not seen before in smart phones. The end user will no longer have to worry about what applications are active or close some programs so that others can run. Android is optimized for low-power, low-memory devices in a fundamental way that no previous platform has attempted. • High-quality graphics and sound: Smooth, antialiased 2D vector graphics and animation inspired by Flash are melded with 3D accelerated OpenGL graphics to enable new kinds of games and business applications. Codecs for the most common industry- standard audio and video formats are built right in, including H.264 (AVC), MP3, and AAC. • Portability across a wide range of current and future hardware: All your programs are written in Java and executed by Android’s Dalvik virtual machine, so your code will be portable across ARM, x86, and other architectures. Support for a variety of input methods is included such as keyboard, touch, and trackball. User interfaces can be customized for any screen resolution and orientation. Android offers a fresh take on the way mobile applications interact with users, along with the technical underpinnings to make it possible. But the best part of Android is the software that you are going to write for it. This book will help you get off to a great start. Who Should Read This Book? The only requirement is a basic understanding of programming in Java or a similar object-oriented language (C# will do in a pinch). You don’t need any prior experience developing software for mobile devices. In fact, if you do, it’s probably best if you try to forget that experience. Android is so different that it’s good to start with an open mind. Report erratum this copy is (P1.0 printing, October 2009)Prepared exclusively for Robert Walsh Download at WoweBook.Com WHAT’SIN THIS BOOK? 12 What’s in This Book? Hello, Android is divided into three parts. Roughly speaking, the book progresses from less advanced to more advanced topics, or from more common to less common aspects of Android. Several chapters share a common example: an Android Sudoku game. By gradually adding features to the game, you’ll learn about many aspects of Android programming including user interfaces, multime- dia, and the Android life cycle. In Part I, we’ll start with an introduction to Android. This is where you’ll learn how to install the Android emulator and how to use an integrated development environment (IDE) to write your first program. Then we’ll introduce a few key concepts like the Android life cycle. Programming in Android is a little different from what you’re probably used to, so make sure you get these concepts before moving on. Part II talks about Android’s user interface, two-dimensional graphics, multimedia components, and simple data access. These features will be used in most programs you write. Part III digs deeper into the Android platform. Here you’ll learn about connecting to the outside world, location-based services, the built-in SQLite database, and three-dimensional graphics. At the end of the book, you’ll find appendices that cover the differences between Android and Java Standard Edition (SE), how to create a wid- get, and publishing your application. What’s New for Cupcake? Android 1.5 (Cupcake) introduced a number of enhancements to the Android platform including support for soft (on-screen) keyboards, video recording, and application widgets. Under the covers, there were more than 1,000 changes to the Android API between 1.1 and 1.5.1 1. http://d.android.com/sdk/api_diff/3/changes.html Report erratum this copy is (P1.0 printing, October 2009)Prepared exclusively for Robert Walsh Download at WoweBook.Com WHAT’S NEWFOR DONUT? 13 To accommodate the new version, every page and example in this book has been reviewed and updated so it will work with 1.5. If you’ve read the first edition of this book, then be sure to check out these chapters in particular: • Chapter 1, Q uick Start, on page 16 includes instructions on using target SDKs and Android Virtual Devices (AVDs). • Chapter 8, L ocating and Sensing, on page 155 now uses the new SensorManager APIs and the new setBuiltInZoomControls( ) method. • Chapter 10, 3 D Graphics in OpenGL, on page 191 has been greatly simplified thanks to the new GLSurfaceView class. In addition, by popular demand we’ve added two new appendixes: • Appendix B, on page 217 shows you how to create a Widget for the Home screen. This is a new feature of Cupcake. • Appendix C, on page 227 guides you through the steps of mak- ing your application available for sale or for free on the Android Market. Android 1.5 (or later) is now available for all shipping Android devices. All new devices have it installed, and Google says that almost all older devices have upgraded. This edition of the book does not cover version 1.1 or earlier. What’s New for Donut? Android 1.6 (Donut) added support for high- and low-density displays, plus a number of minor changes that don’t affect most developers.2 It may be a while before all devices are upgraded to 1.6, so Section C.1, Building for 1.5, 1.6, and Beyond, on page 228 covers how to create a single program that supports multiple versions. All the examples in this book have been tested on both 1.5 and 1.6. Online Resources At the website for this book, http://pragprog.com/titles/eband2, you’ll find the following: • The full source code for all the sample programs used in this book 2. http://d.android.com/sdk/api_diff/4/changes.html Report erratum this copy is (P1.0 printing, October 2009)Prepared exclusively for Robert Walsh Download at WoweBook.Com FAST-FORWARD >> 14 • An errata page, listing any mistakes in the current edition (let’s hope that will be empty!) • A discussion forum where you can communicate directly with the author and other Android developers (let’s hope that will be full!) You are free to use the source code in your own applications as you see fit. Note: If you’re reading the PDF version of this book, you can also click the little gray rectangle before the code listings to download that source file directly. Fast-Forward >> Although most authors expect you to read every word in their books, I know you’re not going to do that. You want to read just enough to let you get something done, and then maybe you’ll come back later and read something else to let you get another piece done. So, I’ve tried to provide you with a little help so you won’t get lost. Each chapter in this book ends with a “Fast-Forward >>” section. These sections will provide some guidance for where you should go next when you need to read the book out of order. You’ll also find pointers to other resources such as books and online documentation here in case you want to learn more about the subject. So, what are you waiting for? The next chapter—Chapter 1, Q uick Start, on page 16—drops you right into the deep end with your first Android program. Chapter 2, K ey Concepts, on page 27 takes a step back and introduces you to the basic concepts and philosophy of Android, and Chapter 3, D esigning the User Interface, on page 41 digs into the user interface, which will be the most important part of most Android programs. Report erratum this copy is (P1.0 printing, October 2009)Prepared exclusively for Robert Walsh Download at WoweBook.Com Part I Introducing Android Prepared exclusively for Robert Walsh Download at WoweBook.Com Chapter 1 Quick Start Android combines the ubiquity of cell phones, the excitement of open source software, and the corporate backing of Google and other Open Handset Alliance members like Intel, TI, T-Mobile, and NTT DoCoMo. The result is a mobile platform you can’t afford not to learn. Luckily, getting started developing with Android is easy. You don’t even need access to an Android phone—just a computer where you can install the Android SDK and phone emulator. In this chapter, I’ll show you how to get all the development tools installed, and then we’ll jump right in and create a working applica- tion: Android’s version of “Hello, World.” 1.1 Installing the Tools The Android software development kit (SDK) works on Windows, Linux, and Mac OS X. The applications you create, of course, can be deployed on any Android devices. Before you start coding, you need to install Java, an IDE, and the Android SDK. Java 5.0+ First you need a copy of Java. All the Android development tools require it, and programs you write will be using the Java language. JDK 5 or 6 is required. It’s not enough to just have a runtime environment (JRE); you need the full development kit. I recommend getting the latest Sun JDK 6.0 Prepared exclusively for Robert Walsh Download at WoweBook.Com INSTALLINGTHE TOOLS 17 update from the Sun download site.1 Mac OS X users should get the latest version of Mac OS X and the JDK from the Apple website. To verify you have the right version, run this command from your shell window. Here’s what I get when I run it: C:\> java -version java version "1.6.0_14" Java(TM) SE Runtime Environment (build 1.6.0_14-b08) Java HotSpot(TM) Client VM (build 14.0-b16, mixed mode, sharing) You should see something similar, with version “1.6.something” or later. Eclipse Next, you should install a Java development environment if you don’t have one already. I recommend Eclipse, because it’s free and because it’s used and supported by the Google developers who created Android. If you don’t want to use Eclipse (there’s always one in every crowd), support for other IDEs such as NetBeans and JetBrains IDEA is avail- able from their respective communities. Or if you’re really old-school, you can forgo an IDE entirely and just use the command-line tools.2 The minimum version of Eclipse is 3.3.1, but you should always use whatever is the most up-to-date production version. Note that you need more than just the standard Eclipse SDK “classic” platform. Go to the Eclipse downloads page,3 and pick “Eclipse IDE for Java Developers.” Follow the directions there for downloading, unpacking, and installing Eclipse into a suitable location (like C:\Eclipse on Windows). Android Next, download the latest Android SDK from Google. The Android down- load page4 has packages for Windows, Mac OS X, and Linux. After downloading the package that’s right for you, unpack the .zip file to a convenient directory (for example, C:\Google). By default, the SDK will be expanded into a subdirectory like android- sdk-windows-1.6_r1. This is your SDK install directory; make a note of the full path so you can refer to it later. 1. http://java.sun.com/javase/downloads 2. S ee http://d.android.com/guide/developing/tools/index.html for documentation on the command-line tools. 3. http://www.eclipse.org/downloads 4. http://d.android.com/sdk Report erratum this copy is (P1.0 printing, October 2009)Prepared exclusively for Robert Walsh Download at WoweBook.Com INSTALLINGTHE TOOLS 18 Figure 1.1: Installing the Android Development Toolkit No special install program is needed but I do recommend you add the SDK’s bin directory to your PATH. The next step is to start Eclipse and configure it. Eclipse Plug-In To make development easier, Google has written a plug-in for Eclipse called the Android Development Toolkit (ADT). To install the plug-in, follow these steps (note these directions are for Eclipse 3.4—different versions may have slightly different menus and options): 1. Start Eclipse, and select Help > Software Updates.... 2. Click the Available Software tab if it’s not already selected. 3. Click the Add Site... button. 4. Enter the location of the Android update site: https://dl-ssl.google. com/android/eclipse/. If you have trouble with this address, try using http in the location instead of https. Once you’ve filled it out, the dialog box should look like Figure 1.1. Click OK. 5. The Android site should now appear in the Available Software view. Select the checkbox next to it, and then click Install.... If you get an error message, then you may not have the right version of Eclipse. I strongly recommend using either the prebuilt Eclipse IDE for Java or the Eclipse IDE for Java EE Development pack- ages, version 3.4 or newer. Report erratum this copy is (P1.0 printing, October 2009)Prepared exclusively for Robert Walsh Download at WoweBook.Com INSTALLINGTHE TOOLS 19 Joe Asks. . . It Says “Connection Error,” So Now What? If you get a connection error, the most likely cause is some kind of firewall erected by your system administrators. To get outside the firewall, you’ll need to configure Eclipse with the address of your proxy server. This is the same proxy server you use for your web browser, but unfortunately Eclipse isn’t smart enough to pick up the setting from there. To tell Eclipse about the proxy, select Preferences > Network Connections, turn on the option for Manual proxy configura- tion, enter the server name and port number, and click OK. If you don’t see the option, you may be running an older ver- sion of Eclipse. Try looking under Preferences > Install/Update, or search the preferences for the word proxy. If you have a custom install of Eclipse, then to use the Android editors you will also need to install the Web Standard Tools (WST) plug-in and all its prerequisites. See the Web Tools platform home page5 for more details and down- load links. These are already built into the recommended packages mentioned earlier. 6. Click Next, accept the license agreements, and then click Finish to start the download and install process. 7. Once the install is done, restart Eclipse. 8. When Eclipse comes back up, you may see a few error messages because you need to tell it where the Android SDK is located. Select Window > Preferences > Android (Eclipse > Preferences on Mac OS X), and enter the SDK install directory you noted earlier. Click OK. Whew! Luckily, you have to do that only once (or at least once every time a new version of ADT or Eclipse comes out). Now that everything is installed, it’s time to write your first program. 5. http://www.eclipse.org/webtools Report erratum this copy is (P1.0 printing, October 2009)Prepared exclusively for Robert Walsh Download at WoweBook.Com CREATING YOUR FIRST PROGRAM 20 1.2 Creating Your First Program ADT comes with a built-in example program, or template, that we’re going to use to create a simple “Hello, Android” program in just a few seconds. Get your stopwatch ready. Ready? Set? Go! Select File > New > Project... to open the New Project dialog box. Then select Android > Android Project, and click Next. Enter the following information: Project name: HelloAndroid Build Target: Android 1.6 Application name: Hello, Android Package name: org.example.hello Create Activity: Hello When you’re done, it should look something like Figure 1.2, on the following page. Click Finish. The Android plug-in will create the project and fill it in with some default files. Eclipse will build it and package it up so it will be ready to execute. If you get an error about missing source folders, select Project > Clean to fix it. OK, that takes care of writing the program; now all that’s left is to try running it. First we’ll run it under the Android Emulator. 1.3 Running on the Emulator To run your Android program, go to the Package Explorer window, right-click the HelloAndroid project, and select Run As > Android Appli- cation. If you’re following along in Eclipse you may see an error dialog like the one in Figure 1.3, on page 22. This indicates we haven’t told the Emulator what kind of phone to emulate. Creating an AVD To do this, you need to create an Android Virtual Device (AVD), using either Eclipse or the android avd command.6 It’s easier to use Eclipse, so select Yes in the AVD Error dialog to open the AVD Manager. You can open the manager again later by selecting Window > Android AVD Manager. 6. http://d.android.com/guide/developing/tools/avd.html Report erratum this copy is (P1.0 printing, October 2009)Prepared exclusively for Robert Walsh Download at WoweBook.Com RUNNINGONTHE EMULATOR 21 Figure 1.2: New Android project Report erratum this copy is (P1.0 printing, October 2009)Prepared exclusively for Robert Walsh Download at WoweBook.Com RUNNINGONTHE EMULATOR 22 Keeping Up with the Plug-In The Android Eclipse plug-in is a work in progress that changes much more often than the Android SDK. The version you down- load may be different than the one I used when writing this book, and it may contain a few, shall we say, idiosyncrasies. I recommend you check the plug-in site monthly to pick up any new features and fixes. Figure 1.3: Missing Android Virtual Device (AVD) In the AVD Manager dialog, fill out the fields for the new AVD as follows: Name: em16 Target: Android 1.6 - API Level 4 SDCard: 128M Skin: Default (HVGA) This tells Eclipse to set up a generic device called “em16,” which has the Android 1.6 (Donut) firmware installed. A 128MB virtual Secure Digital (SD) Card will be allocated, along with a half-VGA (320×480) display. When you’re done you should see something like Figure 1.4, on page 24. Due to updates in the plug-in since this was written your screen may look slightly different. Click Create AVD to create the virtual device. A few seconds later you should see a message that the device has been created. Click OK, and then select the AVD and click Start... to bring it up. Close the AVD Manager window when you’re done. Report erratum this copy is (P1.0 printing, October 2009)Prepared exclusively for Robert Walsh Download at WoweBook.Com RUNNINGONA REAL PHONE 23 Donut vs. Cupcake The version of Android running on your emulator (or real phone) must be compatible with your program’s Build Target. For exam- ple, if you try to run an Android 1.6 (Donut) program on an Android 1.5 (Cupcake) phone, it won’t work because Android 1.5 phones can only run 1.5 or earlier programs. Android 1.6 phones, on the other hand, can run programs built for 1.6, 1.5, and earlier. But it may be a while before most phones have been upgraded. So why not just target Android 1.5? Unfortunately applications built for 1.5 don’t always display correctly on the larger and smaller screens found on 1.6 phones. Luckily there’s an easy way to make your programs compatible with both 1.5 and 1.6. See Section C.1, B uilding for 1.5, 1.6, and Beyond, on page 228 for instructions. Let’s Try That Again Once you have a valid AVD, the Android emulator window will start up and boot the Android operating system. The first time you do this, it may take a minute or two, so be patient. You may need to right-click on the project and select Run As > Android Application again. If you see an error message saying that the application is not responding, select the option to continue waiting. Eclipse will send a copy of your program over to the emulator to exe- cute. The application screen comes up, and your “Hello, Android” pro- gram is now running (see Figure 1.5, on page 25). That’s it! Congratu- lations on your first Android program. 1.4 Running on a Real Phone Running an Android program on a physical device such as the T-Mobile G1 during development is almost identical to running it on the emula- tor. All you need to do is connect your phone to the computer with a USB cable and install a special device driver.7 7. You can find the device driver and installation instructions at http://d.android.com/guide/developing/device.html. Report erratum this copy is (P1.0 printing, October 2009)Prepared exclusively for Robert Walsh Download at WoweBook.Com FAST-FORWARD >> 24 Figure 1.4: Creating an AVD in Eclipse Close the emulator window if it’s already open. As long as the phone is plugged in, applications will be loaded and run there instead. When you’re ready to publish your application for others to use, there are a few more steps you’ll need to take. Appendix C, on page 227 will cover that in more detail. 1.5 Fast-Forward >> Thanks to the Eclipse plug-in, creating a skeletal Android program takes only a few seconds. In Chapter 3, D esigning the User Interface, on page 41, we’ll begin to flesh out that skeleton with a real application—a Sudoku game. This sample will be used in several chapters to demon- strate Android’s API. Report erratum this copy is (P1.0 printing, October 2009)Prepared exclusively for Robert Walsh Download at WoweBook.Com FAST-FORWARD >> 25 Figure 1.5: Running the “Hello, Android” program Shortening the Turnaround Starting the emulator is expensive. Think about it this way— when you first turn on your phone, it needs to boot up just like any computer system. Closing the emulator is just like turning off the phone or pulling the batteries out. So, don’t turn it off! Leave the emulator window running as long as Eclipse is run- ning. The next time you start an Android program, Eclipse will notice the emulator is already there and will just send it the new program to run. Report erratum this copy is (P1.0 printing, October 2009)Prepared exclusively for Robert Walsh Download at WoweBook.Com FAST-FORWARD >> 26 But before delving into that, you should take a few minutes to read Chapter 2, K ey Concepts, on the next page. Once you grasp the basic concepts such as activities and life cycles, the rest will be much easier to understand. Although the use of Eclipse to develop Android programs is optional, I highly recommend it. If you’ve never used Eclipse before, you may want to invest in a quick reference such as the Eclipse IDE Pocket Guide [Bur05]. Report erratum this copy is (P1.0 printing, October 2009)Prepared exclusively for Robert Walsh Download at WoweBook.Com Chapter 2 Key Concepts Now that you have an idea of what Android is, let’s take a look at how it works. Some parts of Android may be familiar, such as the Linux ker- nel, OpenGL, and the SQL database. Others will be completely foreign, such as Android’s idea of the application life cycle. You’ll need a good understanding of these key concepts in order to write well-behaved Android applications, so if you read only one chapter in this book, read this one. 2.1 The Big Picture Let’s start by taking a look at the overall system architecture—the key layers and components that make up the Android open source software stack. In Figure 2.1, on the following page, you can see the “20,000- foot” view of Android. Study it closely—there will be a test tomorrow. Each layer uses the services provided by the layers below it. Starting from the bottom, the following sections highlight the layers provided by Android. Linux Kernel Android is built on top of a solid and proven foundation: the Linux kernel. Created by Linus Torvalds in 1991 while he was a student at the University of Helsinki, Linux can be found today in everything from wristwatches to supercomputers. Linux provides the hardware abstrac- tion layer for Android, allowing Android to be ported to a wide variety of platforms in the future. Prepared exclusively for Robert Walsh Download at WoweBook.Com THE BIG PICTURE 28 Figure 2.1: Android system architecture Internally, Android uses Linux for its memory management, process management, networking, and other operating system services. The Android phone user will never see Linux and your programs will not make Linux calls directly. As a developer, though, you’ll need to be aware it’s there. Some utilities you need during development interact with Linux. For example, the adb shell command1 will open a Linux shell in which you can enter other commands to run on the device. From there you can examine the Linux file system, view active processes, and so forth, sub- ject to security restrictions. Native Libraries The next layer above the kernel contains the Android native libraries. These shared libraries are all written in C or C++, compiled for the particular hardware architecture used by the phone, and preinstalled by the phone vendor. 1. http://d.android.com/guide/developing/tools/adb.html Report erratum this copy is (P1.0 printing, October 2009)Prepared exclusively for Robert Walsh Download at WoweBook.Com THE BIG PICTURE 29 Some of the most important native libraries include the following: • Surface Manager: Android uses a compositing window manager similar to Vista or Compiz, but it’s much simpler. Instead of draw- ing directly to the screen buffer, your drawing commands go into offscreen bitmaps that are then combined with other bitmaps to form the display the user sees. This lets the system create all sorts of interesting effects such as see-through windows and fancy transitions. • 2D and 3D graphics: Two- and three-dimensional elements can be combined in a single user interface with Android. The library will use 3D hardware if the device has it or a fast software renderer if it doesn’t. See Chapter 4, E xploring 2D Graphics, on page 70 and Chapter 10, 3 D Graphics in OpenGL, on page 191. • Media codecs: Android can play video and record and play back audio in a variety of formats including AAC, AVC (H.264), H.263, MP3, and MPEG-4. See Chapter 5, M ultimedia, on page 101 for an example. • SQL database: Android includes the lightweight SQLite database engine,2 the same database used in Firefox and the Apple iPhone. You can use this for persistent storage in your application. See Chapter 9, P utting SQL to Work, on page 171 for an example. • Browser engine: For the fast display of HTML content, Android uses the WebKit library.3 This is the same engine used in the Google Chrome browser, Apple’s Safari browser, the Apple iPhone, and Nokia’s S60 platform. See Chapter 7, T he Connected World, on page 126 for an example. These libraries are not applications that stand by themselves. They exist only to be called by higher level programs. Starting in Android 1.5, you can write and deploy your own native libraries using the Native Development Toolkit (NDK). Native development is beyond the scope of this book, but if you’re interested you can read all about it online.4 2. http://www.sqlite.org 3. http://www.webkit.org 4. http://d.android.com/sdk/ndk/1.6_r1/index.html Report erratum this copy is (P1.0 printing, October 2009)Prepared exclusively for Robert Walsh Download at WoweBook.Com THE BIG PICTURE 30 Joe Asks. . . What’s a Dalvik? Dalvik is a virtual machine (VM) designed and written by Dan Bornstein at Google. Your code gets compiled into machine- independent instructions called bytecodes, which are then executed by the Dalvik VM on the mobile device. Although the bytecode formats are a little different, Dalvik is essentially a Java virtual machine optimized for low memory requirements. It allows multiple VM instances to run at once and takes advantage of the underlying operating system (Linux) for security and process isolation. Bornstein named Dalvik after a fishing village in Iceland where some of his ancestors lived. Android Runtime Also sitting on top of the kernel is the Android runtime, including the Dalvik virtual machine and the core Java libraries. The Dalvik VM is Google’s implementation of Java, optimized for mobile devices. All the code you write for Android will be written in Java and run within the VM. Dalvik differs from traditional Java in two important ways: • The Dalvik VM runs .dex files, which are converted at compile time from standard .class and .jar files. .dex files are more compact and efficient than class files, an important consideration for the limited memory and battery-powered devices that Android targets. • The core Java libraries that come with Android are different from both the Java Standard Edition (Java SE) libraries and the Java Mobile Edition (Java ME) libraries. There is a substantial amount of overlap, however. In Appendix A, on page 213, you’ll find a com- parison of Android and standard Java libraries. Application Framework Sitting above the native libraries and runtime, you’ll find the Applica- tion Framework layer. This layer provides the high-level building blocks Report erratum this copy is (P1.0 printing, October 2009)Prepared exclusively for Robert Walsh Download at WoweBook.Com THE BIG PICTURE 31 you will use to create your applications. The framework comes prein- stalled with Android, but you can also extend it with your own compo- nents as needed. The most important parts of the framework are as follows: • Activity manager: This controls the life cycle of applications (see Section 2.2, I t’s Alive!, on the next page) and maintains a common “backstack” for user navigation. • Content providers: These objects encapsulate data that needs to be shared between applications, such as contacts. See Section 2.3, Content Providers, on page 37. • Resource manager: Resources are anything that goes with your program that is not code. See Section 2.4, U sing Resources, on page 37. • Location manager: An Android phone always knows where it is. See Chapter 8, L ocating and Sensing, on page 155. • Notification manager: Events such as arriving messages, appoint- ments, proximity alerts, alien invasions, and more can be pre- sented in an unobtrusive fashion to the user. Applications and Widgets The highest layer in the Android architecture diagram is the Applica- tions and Widgets layer. Think of this as the tip of the Android iceberg. End users will see only these programs, blissfully unaware of all the action going on below the waterline. As an Android developer, however, you know better. Applications are programs that can take over the whole screen and interact with the user. On the other hand, Widgets (sometimes called gadgets), only operate in a small rectangle of the Home screen applica- tion. The majority of this book will cover application development, because that’s what most of you will be writing. Widget development is covered in Appendix B, on page 217. When someone buys an Android phone, it will come prepackaged with a number of standard system applications, including the following: • Phone dialer • Email Report erratum this copy is (P1.0 printing, October 2009)Prepared exclusively for Robert Walsh Download at WoweBook.Com IT’S ALIVE! 32 Embrace and Extend One of the unique and powerful qualities of Android is that all applications have a level playing field. What I mean is that the system applications have to go through the same public API that you use. You can even tell Android to make your applica- tion replace the standard applications if you want. • Contacts • Web browser • Android Market Using the Android Market, the user will be able to download new pro- grams to run on their phone. That’s where you come in. By the time you finish this book, you’ll be able to write your own killer applications for Android. Now let’s take a closer look at the life cycle of an Android application. It’s a little different from what you’re used to seeing. 2.2 It’s Alive! On your standard Linux or Windows desktop, you can have many appli- cations running and visible at once in different windows. One of the windows has keyboard focus, but otherwise all the programs are equal. You can easily switch between them, but it’s your responsibility as the user to move the windows around so you can see what you’re doing and close programs you don’t need anymore. Android doesn’t work that way. In Android, there is one foreground application, which typically takes over the whole display except for the status line. When the user turns on their phone, the first application they see is the Home application (see Figure 2.2, on the following page). This program typically shows a background image, a search or clock widget, and a scrollable list of other applications the user can invoke. When the user runs an application, Android starts it and brings it to the foreground. From that application, the user might invoke another appli- cation, or another screen in the same application, and then another and Report erratum this copy is (P1.0 printing, October 2009)Prepared exclusively for Robert Walsh Download at WoweBook.Com IT’S ALIVE! 33 Figure 2.2: The Home application another. All these programs and screens are recorded on the applica- tion stack by the system’s Activity Manager. At any time, the user can press the Back button to return to the previous screen on the stack. From the user’s point of view, it works a lot like the history in a web browser. Pressing Back returns them to the previous page. Process != Application Internally, each user interface screen is represented by an Activity class (see Section 2.3, A ctivities, on page 36). Each activity has its own life cycle. An application is one or more activities plus a Linux process to contain them. That sounds pretty straightforward, doesn’t it? But don’t get comfortable yet; I’m about to throw you a curve ball. In Android, an application can be “alive” even if its process has been killed. Put another way, the activity life cycle is not tied to the process life cycle. Processes are just disposable containers for activities. This is Report erratum this copy is (P1.0 printing, October 2009)Prepared exclusively for Robert Walsh Download at WoweBook.Com IT’S ALIVE! 34 Figure 2.3: Life cycle of an Android activity probably different from every other system you’re familiar with, so let’s take a closer look before moving on. Life Cycles of the Rich and Famous During its lifetime, each activity of an Android program can be in one of several states, as shown in Figure 2.3. You, the developer, do not have control over what state your program is in. That’s all managed by the system. However, you do get notified when the state is about to change through the onXX() method calls. You override these methods in your Activity class, and Android will call them at the appropriate time: • onCreate(Bundle): This is called when the activity first starts up. You can use it to perform one-time initialization such as creating the user interface. onCreate( ) takes one parameter that is either Report erratum this copy is (P1.0 printing, October 2009)Prepared exclusively for Robert Walsh Download at WoweBook.Com IT’S ALIVE! 35 null o r some state information previously saved by the onSaveIn- stanceState( ) method. • onStart( ): This indicates the activity is about to be displayed to the user. • onResume( ): This is called when your activity can start interacting with the user. This is a good place to start animations and music. • onPause(): This runs when the activity is about to go into the back- ground, usually because another activity has been launched in front of it. This is where you should save your program’s persis- tent state, such as a database record being edited. • onStop(): This is called when your activity is no longer visible to the user and it won’t be needed for a while. If memory is tight, onStop( ) may never be called (the system may simply terminate your process). • onRestart( ): If this method is called, it indicates your activity is being redisplayed to the user from a stopped state. • onDestroy( ): This is called right before your activity is destroyed. If memory is tight, onDestroy( ) may never be called (the system may simply terminate your process). • onSaveInstanceState(Bundle): Android will call this method to allow the activity to save per-instance state, such as a cursor position within a text field. Usually you won’t need to override it because the default implementation saves the state for all your user inter- face controls automatically. • onRestoreInstanceState(Bundle): This is called when the activity is being reinitialized from a state previously saved by the onSave- InstanceState( ) method. The default implementation restores the state of your user interface. Activities that are not running in the foreground may be stopped or the Linux process that houses them may be killed at any time in order to make room for new activities. This will be a common occurrence, so it’s important that your application be designed from the beginning with this in mind. In some cases, the onPause( ) method may be the last method called in your activity, so that’s where you should save any data you want to keep around for next time. Report erratum this copy is (P1.0 printing, October 2009)Prepared exclusively for Robert Walsh Download at WoweBook.Com BUILDING BLOCKS 36 Flipping the Lid Here’s a quick way to test that your state-saving code is working correctly. In current versions of Android, an orientation change (between portrait and landscape modes) will cause the system to go through the process of saving instance state, pausing, stopping, destroying, and then creating a new instance of the activity with the saved state. On the T-Mobile G1 phone, for example, flipping the lid on the keyboard will trigger this, and on the Android emulator pressing Ctrl+F11 or the 7 or 9 key on the keypad will do it. In addition to managing your program’s life cycle, the Android frame- work provides a number of building blocks that you use to create your applications. Let’s take a look at those next. 2.3 Building Blocks A few objects are defined in the Android SDK that every developer needs to be familiar with. The most important ones are activities, intents, services, and content providers. You’ll see several examples of them in the rest of the book, so I’d like to briefly introduce them now. Activities An a ctivity is a user interface screen. Applications can define one or more activities to handle different phases of the program. As discussed in Section 2.2, I t’s Alive!, on page 32, each activity is responsible for saving its own state so that it can be restored later as part of the application life cycle. See Section 3.3, C reating the Opening Screen, on page 43 for an example. Intents An i ntent is a mechanism for describing a specific action, such as “pick a photo,” “phone home,” or “open the pod bay doors.” In Android, just about everything goes through intents, so you have plenty of opportu- nities to replace or reuse components. See Section 3.5, I mplementing an About Box, on page 54 for an example of an intent. Report erratum this copy is (P1.0 printing, October 2009)Prepared exclusively for Robert Walsh Download at WoweBook.Com USING RESOURCES 37 For example, there is an intent for “send an email.” If your application needs to send mail, you can invoke that intent. Or if you’re writing a new email application, you can register an activity to handle that intent and replace the standard mail program. The next time somebody tries to send an email, they’ll get the option to use your program instead of the standard one. Services A s ervice is a task that runs in the background without the user’s direct interaction, similar to a Unix daemon. For example, consider a music player. The music may be started by an activity, but you want it to keep playing even when the user has moved on to a different program. So, the code that does the actual playing should be in a service. Later, another activity may bind to that service and tell it to switch tracks or stop playing. Android comes with many services built in, along with convenient APIs to access them. Content Providers A c ontent provider is a set of data wrapped up in a custom API to read and write it. This is the best way to share global data between appli- cations. For example, Google provides a content provider for contacts. All the information there—names, addresses, phone numbers, and so forth—can be shared by any application that wants to use it. See Sec- tion 9.5, U sing a ContentProvider, on page 185 for an example. 2.4 Using Resources A resource is a localized text string, bitmap, or other small piece of noncode information that your program needs. At build time all your resources get compiled into your application. You will create and store your resources in the res directory inside your project. The Android resource compiler (aapt)5 processes resources according to which subfolder they are in and the format of the file. For example, PNG and JPG format bitmaps should go in the res/drawable directory, and XML files that describe screen layouts should go in the res/layout directory. 5. http://d.android.com/guide/developing/tools/aapt.html Report erratum this copy is (P1.0 printing, October 2009)Prepared exclusively for Robert Walsh Download at WoweBook.Com SAFEAND SECURE 38 The resource compiler compresses and packs your resources and then generates a class named R that contains identifiers you use to reference those resources in your program. This is a little different from standard Java resources, which are referenced by key strings. Doing it this way allows Android to make sure all your references are valid and saves space by not having to store all those resource keys. Eclipse uses a similar method to store and reference the resources in Eclipse plug-ins. We’ll see an example of the code to access a resource in Chapter 3, Designing the User Interface, on page 41. 2.5 Safe and Secure As mentioned earlier, every application runs in its own Linux process. The hardware forbids one process from accessing another process’s memory. Furthermore, every application is assigned a specific user ID. Any files it creates cannot be read or written by other applications. In addition, access to certain critical operations are restricted, and you must specifically ask for permission to use them in a file named Android- Manifest.xml. When the application is installed, the Package Manager either grants or doesn’t grant the permissions based on certificates and, if necessary, user prompts. Here are some of the most common permissions you will need: • INTERNET: Access the Internet. • READ_CONTACTS: Read (but don’t write) the user’s contacts data. • WRITE_CONTACTS: Write (but don’t read) the user’s contacts data. • RECEIVE_SMS: Monitor incoming SMS (text) messages. • ACCESS_COARSE_LOCATION: Use a coarse location provider such as cell towers or wifi. • ACCESS_FINE_LOCATION: Use a more accurate location provider such as GPS. For example, to monitor incoming SMS messages, you would specify this in the manifest file: Report erratum this copy is (P1.0 printing, October 2009)Prepared exclusively for Robert Walsh Download at WoweBook.Com FAST-FORWARD >> 39 Android can even restrict access to entire parts of the system. Using XML tags in AndroidManifest.xml, you can restrict who can start an activ- ity, start or bind to a service, broadcast intents to a receiver, or access the data in a content provider. This kind of control is beyond the scope of this book, but if you want to learn more, read the online help for the Android security model.6 2.6 Fast-Forward >> The rest of this book will use all the concepts introduced in this chap- ter. In Chapter 3, D esigning the User Interface, on page 41, we’ll use activities and life-cycle methods to define a sample application. Chap- ter 4, E xploring 2D Graphics, on page 70 will use some of the graphics classes in the Android native libraries. Media codecs will be explored in Chapter 5, M ultimedia, on page 101, and content providers will be covered in Chapter 9, P utting SQL to Work, on page 171. 6. http://d.android.com/guide/topics/security/security.html Report erratum this copy is (P1.0 printing, October 2009)Prepared exclusively for Robert Walsh Download at WoweBook.Com Part II Android Basics Prepared exclusively for Robert Walsh Download at WoweBook.Com Chapter 3 Designing the User Interface In Chapter 1, Q uick Start, on page 16, we used the Android Eclipse plug-in to put together a simple “Hello, Android” program in a few min- utes. In Part II, we’ll create a more substantial example: a Sudoku game. By gradually adding features to the game, you’ll learn about many aspects of Android programming. We’ll start with the user inter- face. You can find all the sample code used in this book at http://pragprog. com/titles/eband2. If you’re reading the PDF version of this book, you can click the little gray rectangle before the code listings to download that file directly. 3.1 Introducing the Sudoku Example Sudoku makes a great sample program for Android because the game itself is so simple. You have a grid of eighty-one tiles (nine across and nine down), and you try to fill them in with numbers so that each col- umn, each row, and each of the three-by-three boxes contains the num- bers 1 through 9 only once. When the game starts, some of the numbers (the givens) are already filled in. All the player has to do is supply the rest. A true Sudoku puzzle has only one unique solution. Sudoku is usually played with pencil and paper, but computerized ver- sions are quite popular too. With the paper version, it’s easy to make a mistake early on, and when that happens, you have to go back and erase most of your work. In the Android version, you can change the tiles as often as you like without having to brush away all those pesky eraser shavings. Prepared exclusively for Robert Walsh Download at WoweBook.Com DESIGNINGBY DECLARATION 42 Sudoku Trivia Most people think Sudoku is some kind of ancient Japanese game, but it’s not. Although similar puzzles can be traced to 19th-century French magazines, most experts credit retired American architect Howard Garns with the invention of mod- ern Sudoku. Number Place, as it was known at the time, was first published in the United States in 1979 by Dell Magazines. Android Sudoku (see Figure 3.1, on the next page) will also offer a few hints to take some of the grunt work out of puzzle solving. At one extreme, it could just solve the puzzle for you, but that wouldn’t be any fun, would it? So, we have to balance the hints against the challenge and not make it too easy. 3.2 Designing by Declaration User interfaces can be designed using one of two methods: procedural and declarative. Procedural simply means in code. For example, when you’re programming a Swing application, you write Java code to cre- ate and manipulate all the user interface objects such as JFrame and JButton. Thus, Swing is procedural. Declarative design, on the other hand, does not involve any code. When you’re designing a simple web page, you use HTML, a markup language based on XML that describes what you want to see on the page, not how you want to do it. HTML is declarative. Android tries to straddle the gap between the procedural and declar- ative worlds by letting you create user interfaces in either style. You can stay almost entirely in Java code, or you can stay almost entirely in XML descriptors. If you look up the documentation for any Android user interface component, you’ll see both the Java APIs and the corre- sponding declarative XML attributes that do the same thing. Which should you use? Either way is valid, but Google’s advice is to use declarative XML as much as possible. The XML code is often shorter and easier to understand than the corresponding Java code, and it’s less likely to change in future versions. Report erratum this copy is (P1.0 printing, October 2009)Prepared exclusively for Robert Walsh Download at WoweBook.Com CREATINGTHE OPENING SCREEN 43 Figure 3.1: The Sudoku example program for Android Now let’s see how we can use this information to create the Sudoku opening screen. 3.3 Creating the Opening Screen We’ll start with a skeleton Android program created by the Eclipse plug- in. Just as you did in Section 1.2, C reating Your First Program, on page 20, create a new “Hello, Android” project, but this time use the following values: Project name: Sudoku Build Target: Android 1.6 Application name: Sudoku Package name: org.example.sudoku Create Activity: Sudoku In a real program, of course, you would use your own names here. The package name is particularly important. Each application in the system Report erratum this copy is (P1.0 printing, October 2009)Prepared exclusively for Robert Walsh Download at WoweBook.Com CREATINGTHE OPENING SCREEN 44 must have a unique package name. Once you choose a package name, it’s a little tricky to change it because it’s used in so many places. I like to keep the Android emulator window up all the time and run the program after every change, since it takes only a few seconds. If you do that and run the program now, you’ll see a blank screen that just contains the words “Hello World, Sudoku.” The first order of business is to change that into an opening screen for the game, with buttons to let the player start a new game, continue a previous one, get information about the game, or exit. So, what do we have to change to do that? As discussed in Chapter 2, K eyConcepts, on page 27, Android applica- tions are a loose collection of activities, each of which define a user interface screen. When you create the Sudoku project, the Android plug-in makes a single activity for you in Sudoku.java: Download Sudokuv0/src/org/example/sudoku/Sudoku.java package org.example.sudoku; import android.app.Activity; import android.os.Bundle; public class Sudoku extends Activity { /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); } } Android calls the onCreate() method of your activity to initialize it. The call to setContentView() fills in the contents of the activity’s screen with an Android view widget. We could have used several lines of Java code, and possibly another class or two, to define the user interface procedurally. But instead, the plug-in chose the declarative route, and we’ll continue along those lines. In the previous code, R.layout.main is a resource identifier that refers to the main.xml file in the res/layout directory (see Figure 3.2, on the following page). main.xml declares the user interface in XML, so that’s the file we need to modify. At runtime, Android parses and instanti- ates (inflates) the resource defined there and sets it as the view for the current activity. Report erratum this copy is (P1.0 printing, October 2009)Prepared exclusively for Robert Walsh Download at WoweBook.Com CREATINGTHE OPENING SCREEN 45 Figure 3.2: Initial resources in the Sudoku project It’s important to note that the R class is managed automatically by the Android Eclipse plug-in. When you put a file anywhere in the res direc- tory, the plug-in notices the change and adds resource IDs in R.java in the gen directory for you. If you remove or change a resource file, R.java is kept in sync. If you bring up the file in the editor, it will look something like this: Download Sudokuv0/gen/org/example/sudoku/R.java /* A UTO-GENERATED FILE. DO NOT MODIFY. * * This class was automatically generated by the * aapt tool from the resource data it found. It * should not be modified by hand. */ package org.example.sudoku; Report erratum this copy is (P1.0 printing, October 2009)Prepared exclusively for Robert Walsh Download at WoweBook.Com CREATINGTHE OPENING SCREEN 46 public final class R{ public static final class attr { } public static final class drawable { public static final int icon=0x7f020000; } public static final class layout { public static final int main=0x7f030000; } public static final class string { public static final int app_name=0x7f040001; public static final int hello=0x7f040000; } } The hex numbers are just integers that the Android resource manager uses to load the real data, the strings, and the other assets that are compiled into your package. You don’t need to worry about their values. Just keep in mind that they are handles that refer to the data, not the objects that contain the data. Those objects won’t be inflated until they are needed. Note that almost every Android program, including the base Android framework itself, has an R class. See the online documentation on android.R for all the built-in resources you can use.1 So, now we know we have to modify main.xml. Let’s dissect the origi- nal definition to see what we have to change. Double-click main.xml in Eclipse to open it. Depending on how you have Eclipse set up, you may see either a visual layout editor or an XML editor. In current versions of ADT, the visual layout editor isn’t that useful, so click main.xml or Source tab at the bottom to see the XML. The first line of main.xml is as follows: All Android XML files start with this line. It just tells the compiler that the file is XML format, in UTF-8 encoding. UTF-8 is almost exactly like regular ASCII text, except it has escape codes for non-ASCII characters such as Japanese glyphs. Next we see a reference to : 1. http://d.android.com/reference/android/R.html Report erratum this copy is (P1.0 printing, October 2009)Prepared exclusively for Robert Walsh Download at WoweBook.Com CREATINGTHE OPENING SCREEN 47 Joe Asks. . . Why Does Android Use XML? Isn’t That Inefficient? Android is optimized for mobile devices with limited memory and horsepower, so you may find it strange that it uses XML so pervasively. After all, XML is a verbose, human-readable format not known for its brevity or efficiency, right? Although you see XML when writing your program, the Eclipse plug-in invokes the Android resource compiler, aapt, to prepro- cess the XML into a compressed binary format. It is this format, not the original XML text, that is stored on the device. A layout is a container for one or more child objects and a behavior to position them on the screen within the rectangle of the parent object. Here is a list of the most common layouts provided by Android: • FrameLayout: classArranges its children so they all start at the top left of the screen. This is used for tabbed views and image switchers. • LinearLayout: Arranges its children in a single column or row. This is the most common layout you will use. • RelativeLayout: Arranges its children in relation to each other or to the parent. This is often used in forms. • TableLayout: Arranges its children in rows and columns, similar to an HTML table. Some parameters are common to all layouts: xmlns:android="http://schemas.android.com/apk/res/android" Defines the XML namespace for Android. You should define this once, on the first XML tag in the file. android:layout_width="fill_parent", android:layout_height="fill_parent" Takes up the entire width and height of the parent (in this case, the window). Possible values are fill_parent and wrap_content. Inside the tag you’ll find one child widget: Report erratum this copy is (P1.0 printing, October 2009)Prepared exclusively for Robert Walsh Download at WoweBook.Com CREATINGTHE OPENING SCREEN 48 This defines a simple text label. Let’s replace that with some different text and a few buttons. Here’s our first attempt: Download Sudokuv1/res/layout/main1.xml Report erratum this copy is (P1.0 printing, October 2009)Prepared exclusively for Robert Walsh Download at WoweBook.Com THE RESTOFTHE STORY 91 Next let’s define the Keypad class. Here’s the outline: Download Sudokuv2/src/org/example/sudoku/Keypad.java package org.example.sudoku; import android.app.Dialog; import android.content.Context; import android.os.Bundle; import android.view.KeyEvent; import android.view.View; public class Keypad extends Dialog { protected static final String TAG = "Sudoku"; private final View keys[] = new View[9]; private View keypad; private final int useds[]; private final PuzzleView puzzleView; public Keypad(Context context, int useds[], PuzzleView puzzleView) { super(context); this.useds = useds; this.puzzleView = puzzleView; } Report erratum this copy is (P1.0 printing, October 2009)Prepared exclusively for Robert Walsh Download at WoweBook.Com THE RESTOFTHE STORY 92 @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setTitle(R.string.keypad_title); setContentView(R.layout.keypad); findViews(); for (int element : useds) { if (element != 0) keys[element - 1].setVisibility(View.INVISIBLE); } setListeners(); } // ... } If a particular number is not valid (for example, the same number already appears in that row), then we make the number invisible in the grid so the player can’t select it (see Figure 4.7, on the following page). The findViews( ) method fetches and saves the views for all the keypad keys and the main keypad window: Download Sudokuv2/src/org/example/sudoku/Keypad.java private void findViews() { keypad = findViewById(R.id.keypad); keys[0] = findViewById(R.id.keypad_1); keys[1] = findViewById(R.id.keypad_2); keys[2] = findViewById(R.id.keypad_3); keys[3] = findViewById(R.id.keypad_4); keys[4] = findViewById(R.id.keypad_5); keys[5] = findViewById(R.id.keypad_6); keys[6] = findViewById(R.id.keypad_7); keys[7] = findViewById(R.id.keypad_8); keys[8] = findViewById(R.id.keypad_9); } setListeners( ) loops through all the keypad keys and sets a listener for each one. It also sets a listener for the main keypad window: Download Sudokuv2/src/org/example/sudoku/Keypad.java private void setListeners() { for (int i = 0; i < keys.length; i++) { final int t = i + 1; keys[i].setOnClickListener(new View.OnClickListener(){ public void onClick(View v) { returnResult(t); }}); } Report erratum this copy is (P1.0 printing, October 2009)Prepared exclusively for Robert Walsh Download at WoweBook.Com THE RESTOFTHE STORY 93 Figure 4.7: Invalid values are hidden in the keypad view. keypad.setOnClickListener(new View.OnClickListener(){ public void onClick(View v) { returnResult(0); }}); } When the player selects one of the buttons on the keypad, it calls the returnResult() method with the number for that button. If the player selects a place that doesn’t have a button, then returnResult( ) is called with a zero, indicating the tile should be erased. onKeyDown() is called when the player uses the keyboard to enter a number: Download Sudokuv2/src/org/example/sudoku/Keypad.java @Override public boolean onKeyDown(int keyCode, KeyEvent event) { int tile = 0; Report erratum this copy is (P1.0 printing, October 2009)Prepared exclusively for Robert Walsh Download at WoweBook.Com THE RESTOFTHE STORY 94 switch (keyCode) { case KeyEvent.KEYCODE_0: case KeyEvent.KEYCODE_SPACE: tile = 0; break; case KeyEvent.KEYCODE_1: tile = 1; break; case KeyEvent.KEYCODE_2: tile = 2; break; case KeyEvent.KEYCODE_3: tile = 3; break; case KeyEvent.KEYCODE_4: tile = 4; break; case KeyEvent.KEYCODE_5: tile = 5; break; case KeyEvent.KEYCODE_6: tile = 6; break; case KeyEvent.KEYCODE_7: tile = 7; break; case KeyEvent.KEYCODE_8: tile = 8; break; case KeyEvent.KEYCODE_9: tile = 9; break; default: return super.onKeyDown(keyCode, event); } if (isValid(tile)) { returnResult(tile); } return true; } If the number is valid for the current tile, then it calls returnResult( ); otherwise, the keystroke is ignored. The isValid( ) method checks to see whether the given number is valid for the current position: Download Sudokuv2/src/org/example/sudoku/Keypad.java private boolean isValid(int tile) { for (int t : useds) { if (tile == t) return false; } return true; } If it appears in the used array, then it’s not valid because the same number is already used in the current row, column, or block. The returnResult( ) method is called to return the number selected to the calling activity: Download Sudokuv2/src/org/example/sudoku/Keypad.java /** Return the chosen tile to the caller */ private void returnResult(int tile) { puzzleView.setSelectedTile(tile); dismiss(); } Report erratum this copy is (P1.0 printing, October 2009)Prepared exclusively for Robert Walsh Download at WoweBook.Com THE RESTOFTHE STORY 95 We call the PuzzleView.setSelectedTile() method to change the puzzle’s cur- rent tile. The dismiss call terminates the Keypad dialog box. Now that we have the activity, let’s call it in the Game class and retrieve the result: Download Sudokuv2/src/org/example/sudoku/Game.java /** Open the keypad if there are any valid moves */ protected void showKeypadOrError(int x, int y) { int tiles[] = getUsedTiles(x, y); if (tiles.length == 9) { Toast toast = Toast.makeText(this, R.string.no_moves_label, Toast.LENGTH_SHORT); toast.setGravity(Gravity.CENTER, 0, 0); toast.show(); } else { Log.d(TAG, "showKeypad: used=" + toPuzzleString(tiles)); Dialog v = new Keypad(this, tiles, puzzleView); v.show(); } } To decide which numbers are possible, we pass the Keypad a string in the extraData area containing all the numbers that have already been used. Implementing the Game Logic The rest of the code in Game.java concerns itself with the logic of the game, in particular with determining which are and aren’t valid moves according to the rules. The setTileIfValid( ) method is a key part of that. Given an x and y position and the new value of a tile, it changes the tile only if the value provided is valid. Download Sudokuv2/src/org/example/sudoku/Game.java /** Change the tile only if it's a valid move */ protected boolean setTileIfValid(int x, int y, int value) { int tiles[] = getUsedTiles(x, y); if (value != 0) { for (int tile : tiles) { if (tile == value) return false; } } setTile(x, y, value); calculateUsedTiles(); return true; } Report erratum this copy is (P1.0 printing, October 2009)Prepared exclusively for Robert Walsh Download at WoweBook.Com THE RESTOFTHE STORY 96 To detect valid moves, we create an array for every tile in the grid. For each position, it keeps a list of filled-in tiles that are currently visible from that position. If a number appears on the list, then it won’t be valid for the current tile. The getUsedTiles( ) method retrieves that list for a given tile position: Download Sudokuv2/src/org/example/sudoku/Game.java /** Cache of used tiles */ private final int used[][][] = new int[9][9][]; /** Return cached used tiles visible from the given coords */ protected int[] getUsedTiles(int x, int y) { return used[x][y]; } The array of used tiles is somewhat expensive to compute, so we cache the array and recalculate it only when necessary by calling calculate- UsedTiles( ): Download Sudokuv2/src/org/example/sudoku/Game.java /** Compute the two dimensional array of used tiles */ private void calculateUsedTiles() { for (int x = 0; x < 9; x++) { for (int y = 0; y < 9; y++) { used[x][y] = calculateUsedTiles(x, y); // Log.d(TAG, "used[" + x + "][" + y + "] = " // + toPuzzleString(used[x][y])); } } } calculateUsedTiles( ) simply calls calculateUsedTiles(x, y) on every position in the nine-by-nine grid: Download Sudokuv2/src/org/example/sudoku/Game.java Line 1 /** Compute the used tiles visible from this position */ - private int[] calculateUsedTiles(int x, int y) { - int c[] = new int[9]; - // horizontal 5 for (int i = 0; i < 9; i++) { - if (i == y) - continue; - int t = getTile(x, i); - if (t != 0) 10 c[t - 1] = t; - } - // vertical - for (int i = 0; i < 9; i++) { - if (i == x) 15 continue; Report erratum this copy is (P1.0 printing, October 2009)Prepared exclusively for Robert Walsh Download at WoweBook.Com THE RESTOFTHE STORY 97 - int t = getTile(i, y); - if (t != 0) - c[t - 1] = t; - } 20 // same cell block - int startx = (x / 3) * 3; - int starty = (y / 3) * 3; - for (int i = startx; i < startx + 3; i++) { - for (int j = starty; j < starty + 3; j++) { 25 if (i == x && j == y) - continue; - int t = getTile(i, j); - if (t != 0) - c[t - 1] = t; 30 } - } - // compress - int nused = 0; - for (int t : c) { 35 if (t != 0) - nused++; - } - int c1[] = new int[nused]; - nused = 0; 40 for (int t : c) { - if (t != 0) - c1[nused++] = t; - } - return c1; 45 } We start with an array of nine zeros. On line 5, we check all the tiles on the same horizontal row as the current tile, and if a tile is occupied, we stuff its number into the array: On line 13, we do the same thing for all the tiles on the same vertical column, and on line 21, we do the same for tiles in the three-by-three block. The last step, starting at line 33, is to compress the zeros out of the array before we return it. We do this so that array.length can be used to quickly tell how many used tiles are visible from the current position. Miscellaneous Here are a few other utility functions and variables that round out the implementation. easyPuzzle, mediumPuzzle, and hardPuzzle are our hard- coded Sudoku puzzles for easy, medium, and hard difficulty levels, respectively. Report erratum this copy is (P1.0 printing, October 2009)Prepared exclusively for Robert Walsh Download at WoweBook.Com THE RESTOFTHE STORY 98 Download Sudokuv2/src/org/example/sudoku/Game.java private final String easyPuzzle = "360000000004230800000004200" + "070460003820000014500013020" + "001900000007048300000000045"; private final String mediumPuzzle = "650000070000506000014000005" + "007009000002314700000700800" + "500000630000201000030000097"; private final String hardPuzzle = "009000000080605020501078000" + "000000700706040102004000000" + "000720903090301080000000600"; getPuzzle( ) simply takes a difficulty level and returns a puzzle: Download Sudokuv2/src/org/example/sudoku/Game.java /** Given a difficulty level, come up with a new puzzle */ private int[] getPuzzle(int diff) { String puz; // TODO: Continue last game switch (diff) { case DIFFICULTY_HARD: puz = hardPuzzle; break; case DIFFICULTY_MEDIUM: puz = mediumPuzzle; break; case DIFFICULTY_EASY: default: puz = easyPuzzle; break; } return fromPuzzleString(puz); } Later we’ll change getPuzzle() to implement a continue function. toPuzzleString() converts a puzzle from an array of integers to a string. fromPuzzleString( ) does the opposite. Download Sudokuv2/src/org/example/sudoku/Game.java /** Convert an array into a puzzle string */ static private String toPuzzleString(int[] puz) { StringBuilder buf = new StringBuilder(); for (int element : puz) { buf.append(element); } return buf.toString(); } Report erratum this copy is (P1.0 printing, October 2009)Prepared exclusively for Robert Walsh Download at WoweBook.Com MAKING MORE IMPROVEMENTS 99 /** Convert a puzzle string into an array */ static protected int[] fromPuzzleString(String string) { int[] puz = new int[string.length()]; for (int i = 0; i < puz.length; i++) { puz[i] = string.charAt(i) - '0'; } return puz; } The g etTile( ) method takes x and y positions and returns the number currently occupying that tile. If it’s zero, that means the tile is blank. Download Sudokuv2/src/org/example/sudoku/Game.java /** Return the tile at the given coordinates */ private int getTile(int x, int y) { return puzzle[y * 9 + x]; } /** Change the tile at the given coordinates */ private void setTile(int x, int y, int value) { puzzle[y * 9 + x] = value; } getTileString( ) is used when displaying a tile. It will return either a string with the value of the tile or an empty string if the tile is blank. Download Sudokuv2/src/org/example/sudoku/Game.java /** Return a string for the tile at the given coordinates */ protected String getTileString(int x, int y) { int v = getTile(x, y); if (v == 0) return ""; else return String.valueOf(v); } Once all these pieces are in place, you should have a playable Sudoku game. Give it a try to verify it works. As with any code, though, there is room for improvement. 4.5 Making More Improvements Although the code presented in this chapter performs acceptably for a Sudoku game, more complex programs will likely need to be more carefully written in order to squeeze the last drop of performance out of the device. In particular, the onDraw( ) method is a very performance- critical piece of code, so it’s best to do as little as possible there. Report erratum this copy is (P1.0 printing, October 2009)Prepared exclusively for Robert Walsh Download at WoweBook.Com FAST-FORWARD >> 100 Here are some ideas for speeding up this method: • If possible, avoid doing any object allocations in the method onDraw( ). • Prefetch things such as color constants elsewhere (for example, in the view’s constructor). • Create your Paint objects up front, and just use existing instances in onDraw( ). • For values used multiple times, such as the width returned by getWidth(), retrieve the value at the beginning of the method and then access it from your local copy. As a further exercise for the reader, I encourage you to think about how you could make the Sudoku game graphically richer. For example, you could add some fireworks when the player solves the puzzle or make the tiles spin around like Vanna White does. A moving background behind the puzzle might be interesting. Let your imagination go wild. If you want to make a top-notch product, touches like this can add pizzazz to an otherwise ordinary offering. In Chapter 5, M ultimedia, on the next page, we’ll enhance the pro- gram with a little mood music, and in Chapter 6, S toring Local Data, on page 116, we’ll see how to remember the puzzle state and finally implement that Continue button. 4.6 Fast-Forward >> In this chapter, we just scratched the surface of Android’s graphics capabilities. The native 2D library is quite large, so as you’re actually writing your programs, be sure to take advantage of the tooltips, auto- completion, and Javadoc provided by the Android Eclipse plug-in. The online documentation for the android.graphics3 package goes into much more detail if you need it. If your program needs more advanced graphics, you may want to look ahead a bit and read Chapter 10, 3 D Graphics in OpenGL, on page 191. There you’ll find information on how to use Android’s 3D graphics library, which is based on the OpenGL ES standard. Otherwise, turn to the next chapter for an introduction to the wonderful world of Android audio and video. 3. http://d.android.com/reference/android/graphics/package-summary.html Report erratum this copy is (P1.0 printing, October 2009)Prepared exclusively for Robert Walsh Download at WoweBook.Com Chapter 5 Multimedia Remember those Apple television ads with the silhouette people danc- ing wildly to the beat of their iPods? That’s the kind of excitement you want your products to generate.1 Music, sound effects, and video can make your programs more immersive and engaging than text and graphics alone. This chapter will show you how to add multimedia to your Android application. You may not have your users cavorting in the aisles, but if you do it properly, you can at least put smiles on their faces. 5.1 Playing Audio It was a dark and stormy night.... There goes the starting shot, and they’re off.... The crowd goes wild as State sinks a three-pointer with one second remaining.... Audio cues permeate the environment and set the tempo for our emo- tions. Think of sound as another way to get into your user’s head. Just like you use graphics on the display to convey some information to the user, you can use audio to back that up and reinforce it. Android supports sound and music output through the MediaPlayer class in the android.media package.2 Let’s try it with a simple example that plays sounds when you press a key on the keyboard or D-pad. 1. Of course, normal people older than the age of 8 can’t dance like that. Except perhaps that time when my kids put a lizard in my...but I digress. 2. http://d.android.com/guide/topics/media/index.html Prepared exclusively for Robert Walsh Download at WoweBook.Com PLAYING AUDIO 102 Figure 5.1: Save sound effects in a compressed format that Android can play. We’ll start by creating a “Hello, Android” project, using the following parameters in the New Android Project dialog box: Project name: Audio Build Target: Android 1.6 Application name: Audio Package name: org.example.audio Create Activity: Audio Next we’ll need a few sounds to play. For this example, I created my own with the Windows Sound Recorder program (Start > Programs > Acces- sories > Entertainment > Sound Recorder on Windows XP) and an inex- pensive headset. After getting the sound levels right, I recorded each sound, selected File > Save As... from the menu, clicked the Change... button, and selected a format Android can recognize (see Figure 5.1). You can find all the sound files and source code for these examples on the book’s website. Report erratum this copy is (P1.0 printing, October 2009)Prepared exclusively for Robert Walsh Download at WoweBook.Com PLAYING AUDIO 103 Figure 5.2: Copy audio files into the res/raw directory of your project. Copy the sound files into the res/rawdirectory of your project. As you recall from Section 2.4, U sing Resources, on page 37, simply copying a file into the res directory causes the Android Eclipse plug-in to define a Java symbol for you in the R class. When you’re done, the project should look like Figure 5.2. Now it’s time to fill out the Audio activity. First we declare a new Medi- aPlayer instance for each sound and initialize the instances in the onCre- ate( ) method. Report erratum this copy is (P1.0 printing, October 2009)Prepared exclusively for Robert Walsh Download at WoweBook.Com PLAYING AUDIO 104 Joe Asks. . . What Audio Formats Does Android Support? Well, there’s support on paper, there’s support in the emulator, and there’s support on the actual devices. On paper, Android supports the following file types (this is subject to change with new releases): • WAV (PCM uncompressed) • AAC (Apple iPod format, unprotected) • MP3 (MPEG-3) • WMA (Windows media audio) • AMR (Speech codec) • OGG (Ogg Vorbis)∗ • MIDI (Instruments) In reality, I’ve found that only the OGG, WAV, and MP3 formats work well in the emulator, and thus those are the only ones that I can recommend for application development. Android’s native audio format appears to be 44.1kHz 16-bit stereo. How- ever, since WAV files at that rate are huge, you should just stick to OGG or MP3 files (mono for voice or stereo for music). OGG files seem to work best for short clips like game sound effects. Stay away from unusual rates like 8kHz because the resam- pling artifacts make those rates sound terrible. Use 11kHz, 22kHz, or 44.1kHz sampling rates for the best results. Remember that although the phone may have a tiny speaker, many of your users are going to be plugging in headphones (like an iPod), so you want your audio to be high quality. ∗. http://www.vorbis.com Report erratum this copy is (P1.0 printing, October 2009)Prepared exclusively for Robert Walsh Download at WoweBook.Com PLAYING AUDIO 105 Download Audio/src/org/example/audio/Audio.java package org.example.audio; import android.app.Activity; import android.media.MediaPlayer; import android.os.Bundle; import android.view.KeyEvent; public class Audio extends Activity { private MediaPlayer up, down, left, right, enter; private MediaPlayer a, s, d, f; @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); // Native rate is 44.1kHz 16 bit stereo, but // to save space we just use MPEG-3 22kHz mono up = MediaPlayer.create(this, R.raw.up); down = MediaPlayer.create(this, R.raw.down); left = MediaPlayer.create(this, R.raw.left); right = MediaPlayer.create(this, R.raw.right); enter = MediaPlayer.create(this, R.raw.enter); a = MediaPlayer.create(this, R.raw.a); s = MediaPlayer.create(this, R.raw.s); d = MediaPlayer.create(this, R.raw.d); f = MediaPlayer.create(this, R.raw.f); } } There are other ways to do this; for example, you could declare one MediaPlayer and keep reusing it. This would prevent sounds from over- lapping, though, which may or may not be the effect you want. Another method you may be tempted to try is to create a new Medi- aPlayer whenever you want to make a sound. However, this doesn’t work in practice. For one thing, it slows the program down a little. Worse, in my testing it has a tendency to crash after playing just a few sounds. Therefore, I recommend you stick with the tried-and-true method of setting up your players ahead of time and playing them when needed. Now that we have our sounds loaded up and ready to go, we just need to intercept the key presses and play the right sounds. We do that by overriding the Activity.onKeyDown( ) method. Report erratum this copy is (P1.0 printing, October 2009)Prepared exclusively for Robert Walsh Download at WoweBook.Com PLAYING AUDIO 106 Download Audio/src/org/example/audio/Audio.java Line 1 @Override - public boolean onKeyDown(int keyCode, KeyEvent event) { - MediaPlayer mp; - switch (keyCode) { 5 case KeyEvent.KEYCODE_DPAD_UP: - mp = up; - break; - case KeyEvent.KEYCODE_DPAD_DOWN: - mp = down; 10 break; - case KeyEvent.KEYCODE_DPAD_LEFT: - mp = left; - break; - case KeyEvent.KEYCODE_DPAD_RIGHT: 15 mp = right; - break; - case KeyEvent.KEYCODE_DPAD_CENTER: - case KeyEvent.KEYCODE_ENTER: - mp = enter; 20 break; - case KeyEvent.KEYCODE_A: - mp = a; - break; - case KeyEvent.KEYCODE_S: 25 mp = s; - break; - case KeyEvent.KEYCODE_D: - mp = d; - break; 30 case KeyEvent.KEYCODE_F: - mp = f; - break; - default: - return super.onKeyDown(keyCode, event); 35 } - mp.seekTo(0); - mp.start(); - return true; - } The first part of the method selects a media player based on which key you pressed. Then on line 36, we call the seekTo( ) method to rewind the sound and the start() method to begin playing it. The start( ) method is asynchronous, so it returns immediately regardless of how long the sound lasts. If you like, you can use setOnCompletionListener() to be noti- fied when the clip is finished. Report erratum this copy is (P1.0 printing, October 2009)Prepared exclusively for Robert Walsh Download at WoweBook.Com PLAYING VIDEO 107 When Things Go Wrong If you do much multimedia programming, you’ll soon discover that Android’s MediaPlayer can be a fickle beast. The version in Android 1.5 is much improved over its predecessors but it can still crash at the slightest provocation. One reason this happens is that MediaPlayer is mostly a native application with a thin layer of Java on top of it. The native player code is optimized for performance, and it doesn’t seem to do much error checking. Fortunately, Android’s strong Linux process protections prevent any harm from being done if a crash occurs. The emulator (or the phone if you’re running on a real device) and other appli- cations will continue to run normally. The user would just see the application go away, possibly with a dialog box containing an error message. During development, though, you can get considerably more diagnostic information to help you determine what went wrong. Messages and tracebacks will be printed to the Android system log, which you can view with the LogCat view in Eclipse or the adb logcat command (see Section 3.10, D ebugging with Log Messages, on page 67). If you run the program now and then press one of the keys (for example, the Enter key or the center D-pad key), you should hear a sound. If you don’t hear anything, check your volume control (don’t laugh), or look at the debugging messages in the LogCat view.3 For our next trick, we’ll play a movie using only one line of code. 5.2 Playing Video Video is more than just a bunch of pictures shown one right after another. It’s sound as well, and the sound has to be closely synchro- nized with the images. 3. Audio output may be choppy or delayed in some cases. Try different formats (such as OGG instead of MP3) and lower bit rates. You may also want to investigate using the SoundPool class, which explicitly supports simultaneous streams. It was buggy and poorly documented in the 1.0 release, but as of 1.5 it appears to be stable. Report erratum this copy is (P1.0 printing, October 2009)Prepared exclusively for Robert Walsh Download at WoweBook.Com PLAYING VIDEO 108 Joe Asks. . . What Kind of Video Can You Watch on Android? Here’s what is officially supported: • MP4 (MPEG-4 low bit rate) • H.263 (3GP) • H.264 (AVC) As of Android 1.5, H.263 is the recommended video format because every hardware platform supports it and it’s relatively efficient to encode and decode. It is also compatible with other devices such as the iPhone. You can use a program like QuickTime Pro∗ to convert video from one format to another. Use the lowest resolution and bit rate that you can in order to save space, but don’t set it so low that you sacrifice quality. ∗. http://www.apple.com/quicktime/pro Android’s MediaPlayer class works with video the same way it does with plain audio. The only difference is that you need to create a Surface for the player to use to draw the images. You can use the start( ) and stop() methods to control playback. I’m not going to show you another MediaPlayer example, however, be- cause there is a simpler way to embed videos in your application: the VideoView class. To demonstrate it, create a new Android project called Video using these parameters: Project name: Video Build Target: Android 1.6 Application name: Video Package name: org.example.video Create Activity: Video Change the layout (res/layout/main.xml) to this: Download Videov1/res/layout/main.xml Report erratum this copy is (P1.0 printing, October 2009)Prepared exclusively for Robert Walsh Download at WoweBook.Com PLAYING VIDEO 109 Open V ideo.java, and change the onCreate( ) method as follows: Download Videov1/src/org/example/video/Video.java package org.example.video; import android.app.Activity; import android.os.Bundle; import android.widget.VideoView; public class Video extends Activity { @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); // Fill view from resource setContentView(R.layout.main); VideoView video = (VideoView) findViewById(R.id.video); // Load and start the movie video.setVideoPath("/data/samplevideo.3gp"); video.start(); } } The s etVideoPath() method opens the file, sizes it to its container while preserving the aspect ratio, and begins playing it. Now you need to upload something to play. To do that, run the following command: C:\> adb push c:\code\samplevideo.3gp /data/samplevideo.3gp 1649 KB/s (369870 bytes in 0.219s) You can find samplevideo.3gp in the download package for this book, or you can create one of your own. The directory used here (/data) is just for illustrative purposes and should not really be used for media files. It will only work on the emulator because that directory is protected on real devices. Note that Android doesn’t seem to care what extension you give the file. You can also upload and download files in Eclipse with the File Explorer view in the Android perspective, but I find the command line to be easier for simple things like this. Report erratum this copy is (P1.0 printing, October 2009)Prepared exclusively for Robert Walsh Download at WoweBook.Com PLAYING VIDEO 110 Figure 5.3: Embedding a video is easy with VideoView. There’s one more thing: we’d like the video to take over the whole screen including the title bar and status bar. To do that, all you need to do is specify the right theme in AndroidManifest.xml: Download Videov1/AndroidManifest.xml Report erratum this copy is (P1.0 printing, October 2009)Prepared exclusively for Robert Walsh Download at WoweBook.Com PLAYING VIDEO 111 Joe Asks. . . Why Does It Restart the Video When I Rotate the Display? Android assumes by default that your program knows nothing about screen rotations. To pick up possible resource changes, Android destroys and re-creates your activity from scratch. That means onCreate( ) is called again, which means the video is started again (as this example is currently written). This behavior will be fine for 90 percent of all applications, so most developers will not have to worry about it. It’s even a useful way to test your application life-cycle and state- saving/restoring code (see Section 2.2, I t’s Alive!, on page 32). However, there are a couple of ways to be smarter and opti- mize the transition. The simplest way is to implement onRetainNonConfigurationIn- stance() in your activity to save some data that will be kept across the calls to onDestroy( ) and onCreate( ). When you come back, you use getLastNonConfigurationInstance( ) in the new instance of your activity to recover that information. You can keep anything, even references to your current intent and running threads. The more complicated way is to use the android:configChanges= property in AndroidManifest.xml to inform Android which changes you can handle. For example, if you set it to keyboardHidden|orientation, then Android will not destroy and re-create your activity when the user flips the keyboard. Instead, it will call onConfigurationChanged(Configuration) and assume you know what you’re doing.∗ ∗. For more details, see http://d.android.com/reference/android/app/Activity.html#ConfigurationChanges. Once all that is done, when you run the program, you should see and hear the movie clip (see Figure 5.3, on the preceding page). Try rotating the display to verify it works in both portrait and landscape modes. Voila! Instant video goodness. Now let’s polish up the Sudoku sample with a little mood music. Report erratum this copy is (P1.0 printing, October 2009)Prepared exclusively for Robert Walsh Download at WoweBook.Com ADDING SOUNDSTO SUDOKU 112 Sudoku Trivia Dozens of Sudoku variants exist, although none has gained the popularity of the original. One uses a sixteen-by-sixteen grid, with hexadecimal numbers. Another, called Gattai 5 or Samurai Sudoku, uses five nine-by-nine grids that overlap at the corner regions. 5.3 Adding Sounds to Sudoku In this section, we’re going to take what we’ve learned and add back- ground music to the Sudoku game we’ve been building. One song will play during the opening screen, and another will play during the actual game. This will demonstrate not just how to play music but also some important life-cycle considerations. To add music to the main screen, we just need to override these two methods in the Sudoku class: Download Sudokuv3/src/org/example/sudoku/Sudoku.java @Override protected void onResume() { super.onResume(); Music.play(this, R.raw.main); } @Override protected void onPause() { super.onPause(); Music.stop(this); } If you recall from Section 2.2, I t’s Alive!, on page 32, the o nResume() method is called when the activity is ready to begin interacting with the user. This is a good place to start up the music, so we put a Music.start() call there. The Music class will be defined shortly. R.raw.main refers to res/raw/main.mp3. You can find these sound files in the Sudokuv3 project of the downloadable samples on the book’s website. The onPause( ) method is the paired bookend for onResume( ). Android pauses the current activity prior to resuming a new one, so in Sudoku, Report erratum this copy is (P1.0 printing, October 2009)Prepared exclusively for Robert Walsh Download at WoweBook.Com ADDING SOUNDSTO SUDOKU 113 Joe Asks. . . Shouldn’t We Use a Background Service for Music? We haven’t said much about the Android Service class, but you may have seen it used in some music-playing examples on the Web. Basically, a Service is a way to start a background pro- cess that can run even after your current activity finishes. Ser- vices are similar to, but not quite the same as, Linux daemons. If you’re writing a general-purpose music player and want the music to continue while you’re reading mail or browsing the Web, then, yes, a Service would be appropriate. In most cases, though, you want the music to end when your program ends, so you don’t need to use the Service class. when you start a new game, the Sudoku activity will be paused, and then the Game activity will be started. onPause() will also be called when the user presses the Back or Home key. These are all places where we want our title music to stop, so we call Music.stop( ) in onPause( ). Now let’s do something similar for the music on the Game activity: Download Sudokuv3/src/org/example/sudoku/Game.java @Override protected void onResume() { super.onResume(); Music.play(this, R.raw.game); } @Override protected void onPause() { super.onPause(); Music.stop(this); } If you compare this to what we did to the Sudoku class, you’ll notice that we’re referencing a different sound resource, R.raw.game (res/raw/ game.mp3). Report erratum this copy is (P1.0 printing, October 2009)Prepared exclusively for Robert Walsh Download at WoweBook.Com ADDING SOUNDSTO SUDOKU 114 The final piece of the musical puzzle is the Music class, which will man- age the MediaPlayer class used to play the current music: Download Sudokuv3/src/org/example/sudoku/Music.java Line 1 package org.example.sudoku; - - import android.content.Context; - import android.media.MediaPlayer; 5 - public class Music { - private static MediaPlayer mp = null; - - /** Stop old song and start new one */ 10 public static void play(Context context, int resource) { - stop(context); - mp = MediaPlayer.create(context, resource); - mp.setLooping(true); - mp.start(); 15 } - - /** Stop the music */ - public static void stop(Context context) { - if (mp != null){ 20 mp.stop(); - mp.release(); - mp = null; - } - } 25 } The p lay( ) method first calls the stop( ) method to halt whatever music is currently playing. Next, it creates a new MediaPlayer instance using MediaPlayer.create( ), passing it a context and a resource ID. After we have a player, we then set an option to make it repeat the music in a loop and then start it playing. The start( ) method comes back immediately. The stop() method that begins on line 18 is simple. After a little defen- sive check to make sure we actually have a MediaPlayer to work with, we call its stop( ) and release( ) methods. The MediaPlayer.stop( ) method, strangely enough, stops the music. The release( ) method frees system resources associated with the player. Since those are native resources, we can’t wait until normal Java garbage collection reclaims them. Leav- ing out release( ) is a good way to make your program fail unexpectedly (not that this has ever happened to me, of course; I’m just saying you should keep that in mind). Report erratum this copy is (P1.0 printing, October 2009)Prepared exclusively for Robert Walsh Download at WoweBook.Com FAST-FORWARD >> 115 Now comes the fun part—try playing Sudoku with these changes in place. Stress test it in every way you can imagine, such as switching to different activities, pressing the Back button and the Home button from different points in the game, starting the program when it’s already running at different points, rotating the display, and so forth. Proper life cycle management is a pain sometimes, but your users will appreciate the effort. 5.4 Fast-Forward >> In this chapter, we covered playing audio and video clips using the Android SDK. We didn’t discuss recording because most programs will not need to do that, but if you happen to be the exception, then look up the MediaRecorder class in the online documentation.4 In Chapter 6, S toring Local Data, on the next page, you’ll learn about some simple ways Android programs can store data between invoca- tions. If you don’t need to do that, then you can skip ahead to Chap- ter 7, T he Connected World, on page 126 and learn about network access. 4. http://d.android.com/reference/android/media/MediaRecorder.html Report erratum this copy is (P1.0 printing, October 2009)Prepared exclusively for Robert Walsh Download at WoweBook.Com Chapter 6 Storing Local Data So far, we’ve concentrated on writing applications that don’t need to keep data around when they exit. They start up, run, and go away, leaving no trace that they were ever there. However, most real programs need persistent state, whether it’s a simple font size setting, an embar- rassing photo from your last office party, or next week’s meal plan. Whatever it is, Android lets you permanently store it on your mobile device for later use and protects it from accidental or malicious access by other programs. Your application can store data using several different techniques de- pending on the size of the data, its structure, its lifetime, and whether it will be shared with other programs. In this chapter, we’ll take a look at three simple methods to keep local data: the preferences API, instance state bundles, and flash memory files. In Chapter 9, P utting SQL to Work, on page 171, we’ll delve into more advanced techniques using the built-in SQLite database engine. 6.1 Adding Options to Sudoku In Section 3.7, A dding a Menu, on page 60, we used the onCreateOption- sMenu() method to add a menu containing one item to the main Sudoku screen. When the user presses the Menu key and selects the Settings... item, the code starts the Prefs activity, which lets the user change the options for the game. Because Prefs extends PreferenceActivity, the values for the settings are stored in the program’s preferences area, but orig- inally we didn’t do anything with them. Now we’re going to implement them. Prepared exclusively for Robert Walsh Download at WoweBook.Com ADDING OPTIONSTO SUDOKU 117 Sudoku Trivia There are 6,670,903,752,021,072,936,960 possible classic Sudoku solution grids. If you eliminate duplicates that are just rotations, reflections, or relabelings of each other, you’re left with “only” 5,472,730,538 solutions. First let’s modify the Prefs class to add a couple of getter methods that retrieve the current values of our two options. Here’s the new definition: Download Sudokuv4/src/org/example/sudoku/Prefs.java package org.example.sudoku; import android.content.Context; import android.os.Bundle; import android.preference.PreferenceActivity; import android.preference.PreferenceManager; public class Prefs extends PreferenceActivity { // Option names and default values private static final String OPT_MUSIC = "music"; private static final boolean OPT_MUSIC_DEF = true; private static final String OPT_HINTS = "hints"; private static final boolean OPT_HINTS_DEF = true; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); addPreferencesFromResource(R.xml.settings); } /** Get the current value of the music option */ public static boolean getMusic(Context context) { return PreferenceManager.getDefaultSharedPreferences(context) .getBoolean(OPT_MUSIC, OPT_MUSIC_DEF); } /** Get the current value of the hints option */ public static boolean getHints(Context context) { return PreferenceManager.getDefaultSharedPreferences(context) .getBoolean(OPT_HINTS, OPT_HINTS_DEF); } } Be careful that the option keys (music and hints) match the keys used in res/xml/settings.xml. Report erratum this copy is (P1.0 printing, October 2009)Prepared exclusively for Robert Walsh Download at WoweBook.Com CONTINUINGAN OLD GAME 118 Music.play( )has to be modified to check for the music preference: Download Sudokuv4/src/org/example/sudoku/Music.java /** Stop old song and start new one */ public static void play(Context context, int resource) { stop(context); // Start music only if not disabled in preferences if (Prefs.getMusic(context)) { mp = MediaPlayer.create(context, resource); mp.setLooping(true); mp.start(); } } And P uzzleView.onDraw( ) also needs to be modified to check for the hints preference: Download Sudokuv4/src/org/example/sudoku/PuzzleView.java if (Prefs.getHints(getContext())) { // Draw the hints... } If g etHints() returns true, we draw the highlights for the hints, as shown in Figure 4.6, on page 89. Otherwise, we just skip that part. Next I’ll show you how to use the preferences API to store things other than just options. 6.2 Continuing an Old Game At any time the player can decide to quit playing our Sudoku game and go do something else. Maybe their boss walked in, or they got a phone call or a notification of an important appointment. Whatever the reason, we want to allow the player to come back later and continue where they left off. First we need to save the current state of the puzzle somewhere. The preferences API can be used for more than just options; it can store any small stand-alone bits of information that go with your program. In this case, the state of the puzzle can be saved as a string of eighty- one characters, one for each tile. In the Game class, we’ll start by defining a couple of constants—one for the puzzle data key and one for a flag to tell us to continue the previous game rather than start a new one. Report erratum this copy is (P1.0 printing, October 2009)Prepared exclusively for Robert Walsh Download at WoweBook.Com CONTINUINGAN OLD GAME 119 Download Sudokuv4/src/org/example/sudoku/Game.java private static final String PREF_PUZZLE = "puzzle" ; protected static final int DIFFICULTY_CONTINUE = -1; Next we need to save the current puzzle whenever the game is paused. See Section 2.2, I t’s Alive!, on page 32 for a description of onPause( ) and the other life-cycle methods. Download Sudokuv4/src/org/example/sudoku/Game.java @Override protected void onPause() { super.onPause(); Log.d(TAG, "onPause"); Music.stop(this); // Save the current puzzle getPreferences(MODE_PRIVATE).edit().putString(PREF_PUZZLE, toPuzzleString(puzzle)).commit(); } Now the puzzle is saved, but how do we read the saved data? Remember that when the game is started, the getPuzzle( ) method is called, and the difficulty level is passed in. We’ll use that for continuing as well. Download Sudokuv4/src/org/example/sudoku/Game.java /** Given a difficulty level, come up with a new puzzle */ private int[] getPuzzle(int diff) { String puz; switch (diff) { case DIFFICULTY_CONTINUE: puz = getPreferences(MODE_PRIVATE).getString(PREF_PUZZLE, easyPuzzle); break; // ... } return fromPuzzleString(puz); } All we need to do is add a check for DIFFICULTY_CONTINUE. If that is set, then instead of starting with a fresh puzzle, we read the one we stuffed into the preferences. Next, we need to make the Continue button on the main screen (see Figure 3.4, on page 51) actually do something. Here is where we set that up. Report erratum this copy is (P1.0 printing, October 2009)Prepared exclusively for Robert Walsh Download at WoweBook.Com REMEMBERINGTHE CURRENT POSITION 120 Download Sudokuv4/src/org/example/sudoku/Sudoku.java public void onClick(View v) { switch (v.getId()) { case R.id.continue_button: startGame(Game.DIFFICULTY_CONTINUE); break; // ... } } We added a case in Sudoku.onClick( ) to call startGame() when the Con- tinue button is pressed, passing it DIFFICULTY_CONTINUE. startGame() passes the difficulty to the Game activity, and Game.onCreate( ) calls Intent.getIntExtra( ) to read the difficulty and passes that to getPuzzle() (you can see the code for that in Section 4.2, S tarting the Game, on page 75). There’s one more thing to do: restore from our saved game when our activity goes away and comes back on its own (such as if another activ- ity is started and then the user comes back to the Game activity). This modification to the Game.onCreate() method will take care of that: Download Sudokuv4/src/org/example/sudoku/Game.java @Override protected void onCreate(Bundle savedInstanceState) { // ... // If the activity is restarted, do a continue next time getIntent().putExtra(KEY_DIFFICULTY, DIFFICULTY_CONTINUE); } That pretty much covers it for preferences. Next let’s look at saving instance state. 6.3 Remembering the Current Position If you change the screen orientation while Sudoku is running, you’ll notice that it forgets where its cursor is. That’s because we use a cus- tom PuzzleView view. Normal Android views save their view state auto- matically, but since we made our own, we don’t get that for free. Unlike persistent state, instance state is not permanent. It lives in a Bundle class on Android’s application stack. Instance state is intended to be used for small bits of information such as cursor positions. Report erratum this copy is (P1.0 printing, October 2009)Prepared exclusively for Robert Walsh Download at WoweBook.Com REMEMBERINGTHE CURRENT POSITION 121 Here’s what we have to do to implement it: Download Sudokuv4/src/org/example/sudoku/PuzzleView.java Line 1 import android.os.Bundle; - import android.os.Parcelable; - - public class PuzzleView extends View { 5 private static final String SELX = "selX"; - private static final String SELY = "selY"; - private static final String VIEW_STATE = "viewState"; - private static final int ID = 42; - 10 public PuzzleView(Context context) { - // ... - setId(ID); - } - 15 @Override - protected Parcelable onSaveInstanceState() { - Parcelable p = super.onSaveInstanceState(); - Log.d(TAG, "onSaveInstanceState"); - Bundle bundle = new Bundle(); 20 bundle.putInt(SELX, selX); - bundle.putInt(SELY, selY); - bundle.putParcelable(VIEW_STATE, p); - return bundle; - } 25 @Override - protected void onRestoreInstanceState(Parcelable state) { - Log.d(TAG, "onRestoreInstanceState"); - Bundle bundle = (Bundle) state; - select(bundle.getInt(SELX), bundle.getInt(SELY)); 30 super.onRestoreInstanceState(bundle.getParcelable(VIEW_STATE)); - return; - } - // ... - } On line 5, we define some constants for keys to save and restore the cursor position. We need to save both our own x and y positions, plus any state needed by the underlying View class. As part of Activity.onSaveInstanceState( ) processing, Android will walk down the view hierarchy and call View.onSaveInstanceState( ) on every view it finds that has an ID. The same thing happens for onRestoreIn- stanceState( ). Normally, this ID would come from XML, but since Puzzle- View was created in code, we need to set it ourselves. We make up an arbitrary number on line 8 (any value will do as long as it’s positive) and then use the setId() method to assign it on line 12. Report erratum this copy is (P1.0 printing, October 2009)Prepared exclusively for Robert Walsh Download at WoweBook.Com ACCESSINGTHE INTERNAL FILE SYSTEM 122 The o nSaveInstanceState( ) method is defined on line 16. We call the superclass to get its state, and then we save ours and theirs in a Bundle. Failing to call the superclass will result in a runtime error. Later, onRestoreInstanceState() (line 26) will be called to tease out the information we saved. We get our own x and y positions from the Bundle, and then we call the superclass to let it get whatever it needs. After making these changes, the cursor will be remembered by PuzzleView, just like any other Android view. Next let’s look at keeping data in plain old files. 6.4 Accessing the Internal File System Android runs Linux under the covers, so there’s a real file system mounted in there with a root directory and everything. The files are stored on nonvolatile flash memory built into the device, so they are not lost when the phone is turned off. All of the usual Java file I/O routines from the java.io package are avail- able for your program to use, with the caveat that your process has limited permissions so it can’t mess up any other application’s data. In fact, the main thing it can access is a package private directory created at install time (/data/data/packagename). A few helper methods are provided on the Context class (and thus on the Activity class extended by each of your activities) to let you read and write data there. Here are the ones you’re most likely to need: deleteFile( ) Delete a private file. Returns true if it worked, false otherwise. fileList() Return a list of all files in the application’s private area in a String array. openFileInput( ) Open a private file for reading. Returns a java.io.FileInputStream. openFileOutput() Open a private file for writing. Returns a java.io.FileOutputStream. However, since this internal memory is limited, I recommend you keep the size of any data you put there low, say a megabyte or two at the most, and carefully handle I/O errors when writing in case the space runs out. Luckily, internal memory isn’t the only storage that you have to work with. Report erratum this copy is (P1.0 printing, October 2009)Prepared exclusively for Robert Walsh Download at WoweBook.Com ACCESSINGSDCARDS 123 All in the Family If you recall from Section 2.5, S afe and Secure, on page 38, each application normally gets its own user ID at install time. That user ID is the only one that is allowed to read and write from the application’s private directory. However, if two applica- tions are signed∗ by the same digital certificate, then Android assumes they are from the same developer and gives them the same user ID. On the one hand, that allows them to share all sorts of data with each other if they so choose. But on the other, it also means they’ll need to take special care to stay out of each other’s way. ∗. http://d.android.com/guide/topics/security/security.html#signing 6.5 Accessing SD Cards Some Android devices will include a slot for additional flash memory to be plugged in, typically a Secure Digital (SD) card. These memory cards, if present, are much larger than the built-in memory, and thus they’re ideal for storing multimegabyte music and video files. They cannot be used for code, and every application can read and write files there. In Section 5.2, P laying Video, on page 107, we uploaded a sample video file to the /data directory of the emulated device. This is the wrong place for it, since we’re not supposed to put large files on the internal file system. So, now I’m going to show you a better way. The first step is to create and format a virtual SD card that we can “plug in” to the emulator. Luckily we’ve already done this—if you recall, in Section 1.3, C reating an AVD, on page 20 when we created the “em15” virtual device, we gave it a 128MB virtual SD card as well. You can make it any size you like, but if you make it too small, it may cause the emulator to crash; if you make it too big, you’ll just waste space on your computer’s disk drive. Next, let’s copy the sample video to the SD card: C:\> adb push c:\code\samplevideo.3gp /sdcard/samplevideo.3gp 1468 KB/s (369870 bytes in 0.246s) Report erratum this copy is (P1.0 printing, October 2009)Prepared exclusively for Robert Walsh Download at WoweBook.Com FAST-FORWARD >> 124 Then we need to modify the onCreate( ) method of the Video class to play the movie from the SD card instead of the /data directory: Download Videov2/src/org/example/video/Video.java // Load and start the movie video.setVideoPath("/sdcard/samplevideo.3gp"); video.start(); Now try to run the program. The video should play normally. Note: Starting with Android 1.6 you will need to request the WRITE_ EXTERNAL_STORAGE permission in your manifest file if you want to write to the SD card from your application. Reading from the card doesn’t require any special permissions. 6.6 Fast-Forward >> In this chapter, we covered a couple of basic ways to store local data on the Android platform. That should be enough to get you started, but for structured data such as phone lists and recipes, you’ll need something more advanced. See Chapter 9, P utting SQL to Work, on page 171 for directions on how to use Android’s built-in SQLite database and how to share information between applications using content providers. This brings us to the end of Part II. With the help of the Sudoku exam- ple, you’ve learned all the basics of Android programming, including user interfaces, 2D graphics, audio, video, and simple data storage. Now it’s time to leave Sudoku behind and move beyond the basics. Report erratum this copy is (P1.0 printing, October 2009)Prepared exclusively for Robert Walsh Download at WoweBook.Com Part III Beyond the Basics Prepared exclusively for Robert Walsh Download at WoweBook.Com Chapter 7 The Connected World Over the next few chapters, we’ll cover more advanced topics such as network access and location-based services. You can write many useful applications without these features, but going beyond the basic fea- tures of Android will really help you add value to your programs, giving them much more functionality with a minimum of effort. What do you use your mobile phone for? Aside from making calls, more and more people are using their phones as mobile Internet devices. Analysts predict that in a few years mobile phones will surpass desktop computers as the number-one way to connect to the Internet.1 This point has already been reached in some parts of the world.2 Android phones are well equipped for the new connected world of the mobile Internet. First, Android provides a full-featured web browser based on the WebKit open source project.3 This is the same engine you will find in Google Chrome, the Apple iPhone, and the Safari desktop browser but with a twist. Android lets you use the browser as a compo- nent right inside your application. Second, Android gives your programs access to standard network ser- vices like TCP/IP sockets. This lets you consume web services from Google, Yahoo, Amazon, and many other sources on the Internet. 1. http://www.idc.com/getdoc.jsp?containerId=prUS21303808 2. http://www.comscore.com/press/release.asp?press=1742 3. http://webkit.org Prepared exclusively for Robert Walsh Download at WoweBook.Com BROWSINGBY INTENT 127 Figure 7.1: Opening a browser using an Android intent In this chapter, you’ll learn how to take advantage of all these features and more through four example programs: • BrowserIntent: Demonstrates opening an external web browser using an Android intent • BrowserView: Shows you how to embed a browser directly into your application • LocalBrowser: Explains how JavaScript in an embedded WebView and Java code in your Android program can talk to each other • Translate: Uses data binding, threading, and web services for an amusing purpose 7.1 Browsing by Intent The simplest thing you can do with Android’s networking API is to open a browser on a web page of your choice. You might want to do this to provide a link to your home page from your program or to access some server-based application such as an ordering system. In Android all it takes is three lines of code. To demonstrate, let’s write a new example called BrowserIntent, which will have an edit field where you can enter a URL and a Go button you press to open the browser on that URL (see Figure 7.1). Start by creating a new “Hello, Android” project with the following values in the New Project wizard: Project name: BrowserIntent Build Target: Android 1.6 Application name: BrowserIntent Package name: org.example.browserintent Create Activity: BrowserIntent Report erratum this copy is (P1.0 printing, October 2009)Prepared exclusively for Robert Walsh Download at WoweBook.Com BROWSINGBY INTENT 128 Once you have a the basic program, change the layout file (res/layout/ main.xml) so it looks like this: Download BrowserIntent/res/layout/main.xml