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Android核心模块内容概述

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Android IDE 数据库 C/C++ 20429 次浏览
Android作为一个移动设备的平台,其软件层次结构包括了一个操作系统(OS),中间件(MiddleWare)和应用程序(Application)。

  根据Android的软件框图,其Android核心模块结构自下而上分为以下几个层次:

  第一、操作系统层(OS)

  第二、各种库(Libraries)和Android 运行环境(RunTime)

  第三、应用程序框架(Application Framework)

  第四、应用程序(Application)

  以下分别介绍Andoid各个层次的软件的重点及其相关技术:

  ● Android核心模块之操作系统层(OS)

  Android使用Linux2.6作为操作系统,Linux2.6是一种标准的技术,Linux也是一个开放的操作系统。Android对操作系统的使用包括核心和驱动程序两部分,Android的Linux核心为标准的Linux2.6内核,Android更多的是需要一些与移动设备相关的驱动程序。主要的驱动如下所示:

  显示驱动(Display Driver):常用基于Linux的帧缓冲(Frame Buffer)驱动。

  Flash内存驱动(Flash Memory Driver)

  照相机驱动(Camera Driver):常用基于Linux的v4l(Video for )驱动。

  音频驱动(Audio Driver):常用基于ALSA(Advanced Linux Sound Architecture,高级Linux声音体系)驱动。

  WiFi驱动(Camera Driver):基于IEEE 802.11标准的驱动程序

  键盘驱动(KeyBoard Driver)

  蓝牙驱动(Bluetooth Driver)

  Binder IPC驱动: Andoid一个特殊的驱动程序,具有单独的设备节点,提供进程间通讯的功能。

  Power Management(能源管理)

  ● Android核心模块之各种库(Libraries)和Android 运行环境(RunTime)

  本层次对应一般嵌入式系统,相当于中间件层次。Android的本层次分成两个部分一个是各种库,另一个是Android 运行环境。本层的内容

  大多是使用C++实现的。

  在其中,各种库包括:

  ▅ C库 :C语言的标准库,这也是系统中一个最为底层的库,C库是通过Linux的系统调用来实现。▅ 多媒体框架(MediaFrameword):这部分内容是Android多媒体的核心部分,基于PacketVideo(即PV)的OpenCORE,从功能上本库一共分为两大部分,一个部分是音频、视频的回放(PlayBack),另一部分是则是音视频的纪录(Recorder)。

  ▅ SGL:2D图像引擎。

  ▅ SSL:即Secure Socket Layer位于TCP/IP协议与各种应用层协议之间,为数据通讯提供安全支持。

  ▅ OpenGL ES 1.0 :本部分提供了对3D的支持。

  ▅ 界面管理工具(Surface Management):本部分提供了对管理显示子系统等功能。

  ▅ SQLite:一个通用的嵌入式数据库

  ▅ WebKit:网络浏览器的核心

  ▅ FreeType:位图和矢量字体的功能。

  Android 的各种库一般是以系统中间件的形式提供的,它们均有的一个显着特点就是与移动设备的平台的应用密切相关。

  Android 运行环境主要指的虚拟机技术——Dalvik。Dalvik虚拟机和一般JAVA虚拟机(Java VM)不同,它执行的不是JAVA标准的字节码(bytecode )而是Dalvik可执行格式(.dex)中执行文件。在执行的过程中,每一个应用程序即一个进程(Linux的一个Process)。 二者最大的区别在于Java VM是以基于栈的虚拟机(Stack-based),而Dalvik是基于寄存器的虚拟机(Register-based)。显然,后者最大的好处在于可以根据硬件实现更大的优化,这更适合移动设备的特点。

  ● Android核心模块之应用程序框架(Application Framework)

  Android的应用程序框架为应用程序层的开发者提供APIs,它实际上是一个应用程序的框架。由于上层的应用程序是以JAVA构建的,因此本层次提供的首先包含了UI程序中所需要的各种控件:

  例如: Views (视图组件)包括 lists(列表), grids(栅格), text boxes(文本框), buttons(按钮)等。甚至一个嵌入式的Web浏览器。

  一个Andoid的应用程序可以利用应用程序框架中的以下几个部分:

  Activity (活动)

  Broadcast Intent Receiver (广播意图接收者)

  Service (服务)

  Content Provider (内容提供者)

  ● Android核心模块之应用程序(Application)

  Android的应用程序主要是用户界面(User Interface)方面的,通常以JAVA程序编写,其中还可以包含各种资源文件(放置在res目录中)JAVA程序及相关资源经过编译后,将生成一个APK包。Android本身提供了主屏幕(Home),联系人(Contact),电话(Phone),浏览器(Browers)等众多的核心应用。同时应用程序的开发者还可以使用应用程序框架层的API实现自己的程序。这也是Android开源的巨大潜力的体现。

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