9. Android程序结构HelloAndroid.java是Android工程向导根据Activity名称创建的java文件,这个文件完全可以手工修改。为了在Android系统上显示图形界面,需要使用代码继承Activity类,并在onCreate()函数中声明需要显示的内容
HelloAndroid.java文件的代码如下
package edu.hrbeu.HelloAndroid;
import android.app.Activity;
import android.os.Bundle;
public class HelloAndroid extends Activity {
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
}
}
13. Android程序结构HelloAndroid工程生成的R.java文件的代码package edu.hrbeu.HelloAndroid;
public final class R {
public static final class attr {
}
public static final class drawable {
public static final int icon=0x020000;
}
public static final class layout {
public static final int main=0x030000;
}
public static final class string {
public static final int app_name=0x040001;
public static final int hello=0x040000;
}
}
30. Android程序结构default.properties文件记录Android工程的相关设置,该文件不能手动修改,需右键单击工程名称,选择“Properties”进行修改
在default.properties文件中只有第12行是有效代码,说明Android程序的编译目标# This file is automatically generated by Android Tools.
# Do not modify this file -- YOUR CHANGES WILL BE ERASED!
#
# This file must be checked in Version Control Systems.
#
# To customize properties used by the Ant build system use,
# "build.properties", and override values to adapt the script to your
# project structure.
# Project target.
target=android-3
56. Activity类的帮助信息:public class
Activity
extends ContextThemeWrapper
implements ComponentCallbacks KeyEvent.Callback LayoutInflater.Factory
View.OnCreateContextMenuListener Window.Callback
java.lang.Object
↳ android.content.Context
↳ android.content.ContextWrapper
↳ android.view.ContextThemeWrapper
↳ android.app.Activity
Known Direct Subclasses
ActivityGroup, AliasActivity, ExpandableListActivity, ListActivity
Known Indirect Subclasses
LauncherActivity, PreferenceActivity, TabActivityAndroid API参考文档
57. public class:表示只是一个公开的类;
extends [……]:
标明了这个类继承的父类(Java不支持多继承,因此每个类只有一个唯一的父类),后面的内容表示这个类从祖先开始继承的关系。这里的类使用的是包含了其所在包名称的全名,因此在这里可以得知类及其祖先类属于哪个包;
Implements [……]:
标明了这个类实现的接口(可以有多个);
Known Direct Subclasses [……]:这个类的直接继承者;
Known Indirect Subclasses [……]:这个类的间接继承者。
Android API参考文档