Android之BroadcastReceiver

简介：

BroadcastReceiver本质上就是一种全局的监听器，用于监听系统全局的广播消息，因此它可以非常方便地实现系统中不同组件之间的通信。

特点：

1.BroadcastReceiver用于接收程序所发出的Broadcast Intent，与应用程序启动Activity、Service相同；

2.当应用程序发出一个Broadcast Intent之后，所有匹配该Intent的BroadcastReceiver都有可能被启动；

用法：

网上流行的一张图片可以很好的感受到broadcastreceiver的主要用法：

本次我们通过一个小的示例来一起学习BroadcastReceiver：

建立三个广播类，前两个在manifest里面注册，称为静态注册，最后一个没有在manifest里面注册而在代码中注册，称为动态注册，发送广播的时候有显示发送和隐式发送两种区别。

首先我们来看一下三个广播接收器类的定义以及manifest里面的片段内容如下：

import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.widget.Toast;

public class MyReceiver01 extends BroadcastReceiver{

    @Override
    public void onReceive(Context context, Intent intent) {

        String msg = intent.getExtras().getString("data");

        Toast.makeText(context, "MyReceiver01收到消息：" + msg, Toast.LENGTH_SHORT).show();

    }

}

import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.widget.Toast;

public class MyReceiver02 extends BroadcastReceiver {

    @Override
    public void onReceive(Context context, Intent intent) {
        String msg = intent.getExtras().getString("data");

        Toast.makeText(context, "MyReceiver02收到消息：" + msg, Toast.LENGTH_SHORT)
                .show();
    }

}

public class MyReceiver03 extends BroadcastReceiver {

    public final static String INTENT_ACTION_MYRECEIVER03 = "com.bear.broadcastreceiver.intent.action.receiver03";

    @Override
    public void onReceive(Context context, Intent intent) {
        String msg = intent.getExtras().getString("data");

        Toast.makeText(context, "MyReceiver03收到消息：" + msg, Toast.LENGTH_SHORT)
                .show();

//      abortBroadcast(); 取消广播，后续receiver将无法接收到消息
    }

}

        <receiver android:name="com.bear.broadcastreceiver.MyReceiver01" ></receiver>

        <receiver android:name="com.bear.broadcastreceiver.MyReceiver02">
            <intent-filter >
                <action android:name="com.bear.broadcastreceiver.intent.action.receiver02"/>
            </intent-filter>

        </receiver>

主界面共有5个按钮用来测试，主界面类的定义如下：

import android.app.Activity;
import android.content.Intent;
import android.content.IntentFilter;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;

public class MainActivity extends Activity implements OnClickListener{

    private IntentFilter intentFilter;
    private MyReceiver03 receiver;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        setupViews();

        intentFilter = new IntentFilter(MyReceiver03.INTENT_ACTION_MYRECEIVER03);
        receiver = new MyReceiver03();
    }

    @Override
    public void onClick(View v) {

        switch (v.getId()) {
        case R.id.button1:
            //显式发送广播
            Intent intent = new Intent(MainActivity.this, MyReceiver01.class);
            intent.putExtra("data", "bear");
            sendBroadcast(intent);
            break;
        case R.id.button2:
            //隐式发送广播
            Intent intent02 = new Intent("com.bear.broadcastreceiver.intent.action.receiver02");
            intent02.putExtra("data", "bear02");
            sendBroadcast(intent02);
            break;
        case R.id.button3:
            //动态注册广播
            registerReceiver(receiver, intentFilter);
            break;
        case R.id.button4:
            Intent intent03 = new Intent(MyReceiver03.INTENT_ACTION_MYRECEIVER03);
            intent03.putExtra("data", "bear03");
            sendBroadcast(intent03);
//          sendOrderedBroadcast(intent03, receiverPermission); 按优先级发送广播
            break;
        case R.id.button5:
            //注销广播
            unregisterReceiver(receiver);
            break;

        default:
            break;
        }

    }

    private void setupViews(){
        findViewById(R.id.button1).setOnClickListener(this);
        findViewById(R.id.button2).setOnClickListener(this);
        findViewById(R.id.button3).setOnClickListener(this);
        findViewById(R.id.button4).setOnClickListener(this);
        findViewById(R.id.button5).setOnClickListener(this);

    }

}

总结：

1. 每次系统广播（Broadcast）事件发生后，系统就会创建对应的BroadcastReceiver实例，并自动触发它的onReceive()方法，onReceive()方法执行完后，BroadcastReceiver的实例就会被销毁；

2.如果BroadcastReceiver的onReceive()方法不能在10秒内执行完成，Android会认为该程序无响应。所以不要在广播接收者的onReceive()方法里执行一些耗时的操作，否则会弹出ANR（Application No Response）的对话框；

3.如果确实需要根据广播来完成一项比较耗时的操作，则可以考虑通过Intent启动一个Service来完成该操作。不应考虑使用新线程去完成耗时的操作，因为BroadcastReceiver本身的生命周期极短，可能出现的情况是子线程可能还没有结束，BroadcastReceiver就已经退出了;

Android BroadcastReceiver