BroadcastReceiver 用于异步接收广播Intent。主要有两大类,用于接收广播的:

·         正常广播 Normal broadcasts(用 Context.sendBroadcast()发送)是完全异步的。它们都运行在一个未定义的顺序,通常是在同一时间。这样会更有效,但意味着receiver不能包含所要使用的结果或中止的API  

·         有序广播 Ordered broadcasts(用 Context.sendOrderedBroadcast()发送)每次被发送到一个receiver。所谓有序,就是每个receiver执行后可以传播到下一个receiver,也可以完全中止传播——不传播给其他receiver。 而receiver运行的顺序可以通过matched intent-filter 里面的android:priority来控制,当priority优先级相同的时候,Receiver以任意的顺序运行。

 

    要注意的是,即使是Normal broadcasts,系统在某些情况下可能会恢复到一次传播给一个receiver。 特别是receiver可能需要创建一个进程,为了避免系统超载,只能一次运行一个receiver

 

    Broadcast Receiver 并没有提供可视化的界面来显示广播信息。可以使用NotificationNotification Manager来实现可视化的信息的界面,显示广播信息的内容,图标及震动信息。

 

生命周期

    一个BroadcastReceiver 对象只有在被调用onReceive(Context, Intent)的才有效的,当从该函数返回后,该对象就无效的了,结束生命周期。

    因此从这个特征可以看出,在所调用的onReceive(Context, Intent)函数里,不能有过于耗时的操作,不能使用线程来执行。对于耗时的操作,请start service来完成。因为当得到其他异步操作所返回的结果时,BroadcastReceiver 可能已经无效了。

 

发送广播

    事件的广播比较简单,构建Intent对象,可调用sendBroadcast(Intent)方法将广播发出。另外还有sendOrderedBroadcast()sendStickyBroadcast()等方法,请查阅API Doc

    1.new Intent with action name 

        Intent intent = new Intent(String action);

      或者 只是new Intent, 然后

        intent.setAction(String action);

 

    2.set data等准备好了后,in activity,

        sendBroadcast(Intent); // 发送广播

 

接收广播

    通过定义一个继承BroadcastReceiver类来实现,继承该类后覆盖其onReceiver方法,并在该方法中响应事件。

public class SMSReceiver extends BroadcastReceiver {

        @Override
        
public void onReceive(Context context, Intent intent)
                
// get data from SMS intent
                Bundle bundle = intent.getExtras();
                
if (bundle != null){
                        
// get message by "pdus"
                        Object[] objArray = (Object[]) bundle.get(
"pdus");

                        
// rebuild SMS
                        SmsMessage[] messages =
new SmsMessage[objArray.length];
                        
for (int i=0; i < objArray.length; i++){
                                messages[i] = SmsMessage.createFromPdu((
byte[])objArray[i]);

                                StringBuilder str =
new StringBuilder("from: ");
                                str.append(messages[i].getDisplayOriginatingAddress());
                                str.append(
"\nmessage:\n");
                                str.append(messages[i].getDisplayMessageBody());

                                Toast.makeText(context, str.toString(), Toast.LENGTH_LONG)
                                                .show();
                        }
                }
        }
}

 

注册Receiver

   注册有两种方式:
   1.
静态方式,在AndroidManifest.xmlapplication里面定义receiver并设置要接收的action

<receiver android:name=".SMSReceiver">
        
<intent-filter>
                
<action android:name="android.provider.Telephony.SMS_RECEIVED" />
        
</intent-filter>
</receiver>


   2.
动态方式, activity里面调用函数来注册,和静态的内容差不多。一个形参是receiver,另一个是IntentFilter,其中里面是要接收的action

public class HelloDemo extends Activity {    
        
private BroadcastReceiver receiver;    

        @Override
        
protected void onStart() {
                
super.onStart();

                receiver =
new CallReceiver();
                registerReceiver(receiver,
new IntentFilter("android.intent.action.PHONE_STATE"));
        }

        @Override
        
protected void onStop() {
                unregisterReceiver(receiver);
                
super.onStop();
        }
}

   一个receiver可以接收多个action的,即可以有多个intent-filter,需要在onReceive里面对intent.getAction(action name)进行判断。
 

    个人推荐使用静态注册方式,由系统来管理receiver,而且程序里的所有receiver,可以在xml里面一目了然。而动态注册方式,隐藏在代码中,比较难发现。
   
而且动态注册,需要特别注意的是,在退出程序前要记得调用
Context.unregisterReceiver()方法。一般在activityonStart()里面进行注册, onStop()里面进行注销。官方提醒,如果在Activity.onResume()里面注册了,就必须在Activity.onPause()注销。

 

Permission权限
 
要接收某些action,需要在AndroidManifest.xml里面添加相应的permission。例如接收SMS:

<uses-permission android:name="android.permission.RECEIVE_SMS" />



下面给出动态注册的接收来电的广播处理的CallReceiver的代码:

   一种方式是直接读取intent.getStringExtra("incoming_number")来获取来电号码:

public class CallReceiver extends BroadcastReceiver {

        @Override
        
public void onReceive(Context context, Intent intent) {
                TelephonyManager teleManager = (TelephonyManager) context.getSystemService(Context.TELEPHONY_SERVICE);
                
                
switch(teleManager.getCallState()){
                
case TelephonyManager.CALL_STATE_RINGING: //响铃
                        Toast.makeText(context,
"Ringing: " + intent.getStringExtra("incoming_number"), Toast.LENGTH_LONG).show();
                        
break;
                
case TelephonyManager.CALL_STATE_OFFHOOK: //接听
                        Toast.makeText(context,
"OffHook: " + intent.getStringExtra("incoming_number"), Toast.LENGTH_LONG).show();
                        
break;
                
case TelephonyManager.CALL_STATE_IDLE: //挂断
                        Toast.makeText(m_context,
"Idle: " + incomingNumber, Toast.LENGTH_LONG).show();
                        
break;
                }
        }
}

   在运行时,发现除了响铃时可以获取来电号码,接听和挂断都不能成功获取的,显示为null

 

   另一种方式是通过PhoneStateListeneronCallStateChanged来监听状态的变化:

public class CallReceiver extends BroadcastReceiver {

        
private Context m_context;
        @Override
        
public void onReceive(Context context, Intent intent) {
                m_context = context;
                TelephonyManager teleManager = (TelephonyManager) context.getSystemService(Context.TELEPHONY_SERVICE);
                teleManager.listen(
new PhoneStateListener(){

                        @Override
                        
public void onCallStateChanged(int state, String incomingNumber) {
                                
switch(state){
                                
case TelephonyManager.CALL_STATE_RINGING: //响铃
                                        Toast.makeText(m_context,
"Ringing: " + incomingNumber, Toast.LENGTH_LONG)
                                                                .show();
                                        
break;
                                
case TelephonyManager.CALL_STATE_OFFHOOK: //接听
                                        Toast.makeText(m_context,
"OffHook: " + incomingNumber, Toast.LENGTH_LONG)
                                        .show();
                                        
break;
                                
case TelephonyManager.CALL_STATE_IDLE: //挂断
                                        Toast.makeText(m_context,
"Idle: " + incomingNumber, Toast.LENGTH_LONG)
                                        .show();
                                        
break;
                                }
                        }}, PhoneStateListener.LISTEN_CALL_STATE);  
        }
}

    运行时也发现incomingNumber在接听和挂断时获取为blank

    因为这里监听的是通话的状态变化,所以这个receiver会被调用3次。

 

    监听通话状态需要加上权限:

<uses-permission android:name="android.permission.READ_PHONE_STATE"/>

 

===========

小结:

1. 对于sendBroadCastintent对象,需要设置其action name 
2.
推荐使用显式指明receiver,在配置文件AndroidManifest.xml指明; 
3.
一个receiver可以接收多个action; 

4. 每次接收广播都会重新生成一个接收广播的对象,再次调用onReceive

5. BroadCast 中尽量不要处理太多逻辑问题,建议复杂的逻辑交给Activity 或者 Service 去处理。