BroadcastReceiver

 

• 广播有两种注册方式：静态注册和动态注册。静态注册是在AndroidManifest中注册，在应用安装的时候会被系统解析，这种广播不需要应用启动就可以收到相应的广播。动态注册需要通过Context.registerReceiver()来注册，这种广播需要应用启动才能注册并接收广播。
• 实现不同组件之间的通信；一对多通信
• 与Activity组件不同的是，当系统通过Intent启动指定了Activity组件时，如果系统没有找到合适的Activity组件，会导致程序异常中止；但系统通过Intent激发BroadcastReceiver时，如果找不到合适的BroadcastReceiver组件，应用不会有任何问题
• BroadcastReceiver属于系统级的监听器，它拥有自己的进程，只要存在与之匹配的Broadcast被以Intent的形式发送出来，BroadcastReceiver就会被激活。当在系统注册一个BroadcastReceiver之后，每次系统以一个Intent的形式发布Broadcast的时候，系统都会创建与之对应的BroadcastReceiver广播接收者实例，并自动触发它的onReceive()方法，当onReceive()方法被执行完成之后，BroadcastReceiver的实例就会被销毁。
• 虽然它独自享用一个单独的进程，但也不是没有限制的，如果BroadcastReceiver.onReceive()方法不能在10秒内执行完成，Android系统就会认为该BroadcastReceiver对象无响应，然后弹出ANR（Application No Response）对话框，所以不要在BroadcastReceiver.onReceive()方法内执行一些耗时的操作。如果需要根据广播内容完成一些耗时的操作，一般考虑通过Intent启动一个Service（或其他组建）来完成该操作，而不应该在BroadcastReceiver中开启一个新线程完成耗时的操作，因为BroadcastReceiver本身的生命周期很短，可能出现的情况是子线程还没有结束，BroadcastReceiver就已经退出的情况，而如果BroadcastReceiver所在的进程结束了，该线程就会被标记为一个空线程，根据Android的内存管理策略，在系统内存紧张的时候，会按照优先级，结束优先级低的线程，而空线程无异是优先级最低的，这样就可能导致BroadcastReceiver启动的子线程不能执行完成。

 

由于涉及不同app，注意安全机制（查看官网（网））：

If you don't need to send broadcasts across applications, consider using this class with LocalBroadcastManager instead of the more general facilities described below. This will give you a much more efficient implementation (no cross-process communication needed) and allow you to avoid thinking about any security issues related to other applications being able to receive or send your broadcasts.

 

 

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普通广播

Normal Broadcast

它是完全异步的，在逻辑上，当一个Broadcast被发出之后，所有的与之匹配的BroadcastReceiver都同时接收到Broadcast。

优点：传递效率比较高

缺点：一个BroadcastReceiver不能影响其他响应这条Broadcast的BroadcastReceiver

 

• BroadcastReceiver

发送方：

1. publicvoid broadcastIntent(View view)
2. {
3.    Intent intent =newIntent();
4.    intent.setAction("com.tutorialspoint.CUSTOM_INTENT");
5.    sendBroadcast(intent);
6. }

接收方：

1. //定义：
2. publicclassMyReceiver extends BroadcastReceiver{
3.    @Override
4.    publicvoid onReceive(Context context,Intent intent){
5.       Toast.makeText(context,"Intent Detected.",Toast.LENGTH_LONG).show();
6.    }
7. }

注册：

1. //静态注册：
2. <receiverandroid:name="MyReceiver">
3.  
4.       <intent-filter>
5.          <actionandroid:name="com.tutorialspoint.CUSTOM_INTENT">
6.          </action>
7.       </intent-filter>
8.  
9.    </receiver>

 

1. //动态注册：
2. IntentFilter filter  =newIntentFilter("com.tutorialspoint.CUSTOM_INTENT");
3. MyReceiver receiver =new MyReceiver();
4. Context.registerReceiver(receiver, filter );
5. Context.unregisterReceiver(receiver);

 

Note:   

•  If registering a receiver in your Activity.onResume() implementation, you should unregister it in Activity.onPause(). (You won't receive intents when paused, and this will cut down on unnecessary system overhead). 
• Do not unregister in Activity.onSaveInstanceState(), because this won't be called if the user moves back in the history stack.

 

 

• LocalBroadcastManager

LocalBroadcastManager（网）

Helper to register for and send broadcasts of Intents to local objects within your process. This is has a number of advantages over sending global broadcasts with sendBroadcast(Intent)。

static LocalBroadcastManager	getInstance(Context context)
void	registerReceiver(BroadcastReceiver receiver, IntentFilter filter) Register a receive for any local broadcasts that match the given IntentFilter.
boolean	sendBroadcast(Intent intent) Broadcast the given intent to all interested BroadcastReceivers.
void	sendBroadcastSync(Intent intent) Like sendBroadcast(Intent), but if there are any receivers for the Intent this function will block and immediately dispatch them before returning.
void	unregisterReceiver(BroadcastReceiver receiver) Unregister a previously registered BroadcastReceiver.

 

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有序广播

Ordered Broadcast

它是同步执行的，有序广播的接收器将会按照预先声明的优先级依次接受Broadcast，是链式结构，优先级越高（-1000~1000），越先被执行。优先级高的接收器，可以把执行结果传入下一个接收器中，也可以终止Broadcast的传播（通过abortBroadcast()方法），一旦Broadcast的传播被终止，优先级低于它的接收器就不会再接收到这条Broadcast了。

 

Context.sendOrderedBroadcast()：发送有序广播。（其他与上边同）

 

系统广播

拦截软件的原理

 

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参考

Android--广播BroadcastReceiver （网）（BroadcastReceiver基础概念、种类、Demo）

 

 

 

来自为知笔记(Wiz)