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背景知识：当Android启动时，会发出一个系统广播，内容为ACTION_BOOT_COMPLETED，它的字符串常量表示为 android.intent.action.BOOT_COMPLETED。只要在程序中“捕捉”到这个消息，再启动之即可。记住，Android框架说：Don't call me, I'll call you back。我们要做的是做好接收这个消息的准备，而实现的手段就是实现一个BroadcastReceiver。
代码解析：
1、界面Activity：SayHello.java
package com.apkabc.BootStartDemo;
import android.app.Activity;
import android.os.Bundle;
import android.widget.TextView;
public class SayHello extends Activity {
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
TextView tv = new TextView(this);
tv.setText("Hello. I started!");
setContentView(tv);
}
}
package com.apkabc.BootStartDemo;
import android.app.Activity;
import android.os.Bundle;
import android.widget.TextView;
public class SayHello extends Activity {
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
TextView tv = new TextView(this);
tv.setText("Hello. I started!");
setContentView(tv);
}
}
这段代码很简单，当Activity启动时，创建一个TextView，用它显示"Hello. I started!"字样。
2、接收广播消息：BootBroadcastReceiver.java
package com.apkabc.BootStartDemo;
import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
public class BootBroadcastReceiver extends BroadcastReceiver {
static final String ACTION = "android.intent.action.BOOT_COMPLETED";
@Override
public void onReceive(Context context, Intent intent) {
if (intent.getAction().equals(ACTION)){
Intent sayHelloIntent=new Intent(context,SayHello.class);
sayHelloIntent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
context.startActivity(sayHelloIntent);
}
}
}
package com.apkabc.BootStartDemo;
import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
public class BootBroadcastReceiver extends BroadcastReceiver {
static final String ACTION = "android.intent.action.BOOT_COMPLETED";
@Override
public void onReceive(Context context, Intent intent) {
if (intent.getAction().equals(ACTION)){
Intent sayHelloIntent=new Intent(context,SayHello.class);
sayHelloIntent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
context.startActivity(sayHelloIntent);
}
}
}
该类派生自BroadcastReceiver，覆载方法onReceive中，检测接收到的Intent是否符合BOOT_COMPLETED，如果符合，则启动SayHello那个Activity。
3、配置文件：AndroidManifest.xml
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.apkabc.BootStartDemo"
android:versionCode="1"
android:versionName="1.0">
<application android:icon="@drawable/icon" android:label="@string/app_name">
<activity android:name=".SayHello"
android:label="@string/app_name">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<receiver android:name=".BootBroadcastReceiver">
<intent-filter>
<action android:name="android.intent.action.BOOT_COMPLETED" />
</intent-filter>
</receiver>
</application>
<uses-sdk android:minSdkVersion="3" />
<uses-permission android:name="android.permission.RECEIVE_BOOT_COMPLETED"></uses-permission>
</manifest>
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.apkabc.BootStartDemo"
android:versionCode="1"
android:versionName="1.0">
<application android:icon="@drawable/icon" android:label="@string/app_name">
<activity android:name=".SayHello"
android:label="@string/app_name">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<receiver android:name=".BootBroadcastReceiver">
<intent-filter>
<action android:name="android.intent.action.BOOT_COMPLETED" />
</intent-filter>
</receiver>
</application>
<uses-sdk android:minSdkVersion="3" />
<uses-permission android:name="android.permission.RECEIVE_BOOT_COMPLETED"></uses-permission>
</manifest>
注意其中粗体字那一部分，该节点向系统注册了一个receiver，子节点intent-filter表示接收 android.intent.action.BOOT_COMPLETED消息。不要忘记配置 android.permission.RECEIVE_BOOT_COMPLETED权限。
延伸思考：在多数情况下，要自动运行的不是有界面的程序，而是在后台运行的service。此时，就要用startService来启动相应的 service了。 | 
转播
