Broadcast 是一种被用于应用内和应用之间传递信息的机制。一个广播可以对应多个接受者。一个完整的广播机制，需要具有以下三个要素：
- 发送广播的Broadcast
- 接受广播的BroadcastReceiver
- 传递信息的Intent
广播的注册分为静态注册和动态注册：
- 静态注册：静态注册的广播是指在AndroidManifest中注册的广播，此种广播在应用安装时就被系统解析，不需要启动应用就可以收到相应的广播。
<receiver android:name=".broadcast.MyBroadcastReceiver">
<intent-filter>
<action android:name="MY_BROADCAST_RECEIVER" />
</intent-filter>
</receiver>动态注册：通过Context.registerReceiver()来实现，不需要时要通过Context.unRegisterReceiver()解除广播，此种广播必须应用启动后才能注册并接收广播。
// 动态注册广播接收器 registerReceiver(new DynamicBroadcastReceiver(), new IntentFilter(MyBroadcastReceiver.ACTION));
广播又分为普通广播、有序广播、本地广播和sticky广播。
一、普通广播
普通广播通过Context.sendBroadcast()发送，我们没有办法制定Receiver们对于普通广播的接收顺序。理论上所有的接收器（Receiver）接收到广播的顺序不确定，但一般是按照其在AndroidMainfest.xml文件中注册的顺序（不绝对）。
普通广播中，接受者不能将处理结果传递给下一个接收器，也无法终止广播的传播。
如下代码是一个静态注册的广播示例：
public class MyBroadcastReceiver extends BroadcastReceiver {
String TAG = MyBroadcastReceiver.class.getSimpleName();
public static final String ACTION = "MY_BROADCAST_RECEIVER";
@Override
public void onReceive(Context context, Intent intent) {
Log.i(TAG, "接收到广播消息：" + intent.getStringExtra(BroadcastTestActivity.INTENT_INFO));
}
}然后再AndroidMainfest.xml中注册这个广播:
<receiver android:name=".broadcast.MyBroadcastReceiver">
<intent-filter>
<action android:name="MY_BROADCAST_RECEIVER" />
</intent-filter>
</receiver>接下来在Activity中调用Context.sendBroadcast()发送广播就可以了：
Intent intent = new Intent(MyBroadcastReceiver.ACTION);
intent.putExtra(INTENT_INFO, "我是一个普通广播");
sendBroadcast(intent);log如下：
12-08 17:29:44.259 6644-6644/cn.codingblock.androidadvancestudy I/MyBroadcastReceiver: 接收到广播消息：我是一个普通广播- 普通广播的接收顺序测试
我们仿照MyBroadcastReciver创建多个接收器，代码一样：
/**
* 静态注册的广播接收器2
* Created by liuwei on 17/12/7.
*/
public class MyBroadcast2Receiver extends BroadcastReceiver {
String TAG = MyBroadcast2Receiver.class.getSimpleName();
public static final String ACTION = "MY_BROADCAST_RECEIVER";
@Override
public void onReceive(Context context, Intent intent) {
Log.i(TAG, "接收到广播消息：" + intent.getStringExtra(BroadcastTestActivity.INTENT_INFO));
}
}
/**
* 静态注册的广播接收器3
* Created by liuwei on 17/12/7.
*/
public class MyBroadcast3Receiver extends BroadcastReceiver {...}
/**
* 静态注册的广播接收器4
* Created by liuwei on 17/12/7.
*/
public class MyBroadcast4Receiver extends BroadcastReceiver {...}
/**
* 静态注册的广播接收器5
* Created by liuwei on 17/12/7.
*/
public class MyBroadcast5Receiver extends BroadcastReceiver {...}
/**
* 静态注册的广播接收器6
* Created by liuwei on 17/12/7.
*/
public class MyBroadcast6Receiver extends BroadcastReceiver {...}然后在AndroidMainfest.xml中为以上广播都注册同一个action
<receiver android:name=".broadcast.MyBroadcastReceiver">
<intent-filter>
<action android:name="MY_BROADCAST_RECEIVER" />
</intent-filter>
</receiver>
<receiver android:name=".broadcast.MyBroadcast6Receiver">
<intent-filter>
<action android:name="MY_BROADCAST_RECEIVER" />
</intent-filter>
</receiver>
<receiver android:name=".broadcast.MyBroadcast2Receiver">
<intent-filter>
<action android:name="MY_BROADCAST_RECEIVER" />
</intent-filter>
</receiver>
<receiver android:name=".broadcast.MyBroadcast3Receiver">
<intent-filter>
<action android:name="MY_BROADCAST_RECEIVER" />
</intent-filter>
</receiver>
<receiver android:name=".broadcast.MyBroadcast4Receiver">
<intent-filter>
<action android:name="MY_BROADCAST_RECEIVER" />
</intent-filter>
</receiver>
<receiver android:name=".broadcast.MyBroadcast5Receiver">
<intent-filter>
<action android:name="MY_BROADCAST_RECEIVER" />
</intent-filter>
</receiver>点击发送广播，查看log：
12-08 17:29:44.259 6644-6644/cn.codingblock.androidadvancestudy I/MyBroadcastReceiver: 接收到广播消息：我是一个普通广播
12-08 17:29:44.268 6644-6644/cn.codingblock.androidadvancestudy I/MyBroadcast6Receiver: 接收到广播消息：我是一个普通广播
12-08 17:29:44.271 6644-6644/cn.codingblock.androidadvancestudy I/MyBroadcast2Receiver: 接收到广播消息：我是一个普通广播
12-08 17:29:44.273 6644-6644/cn.codingblock.androidadvancestudy I/MyBroadcast3Receiver: 接收到广播消息：我是一个普通广播
12-08 17:29:44.277 6644-6644/cn.codingblock.androidadvancestudy I/MyBroadcast4Receiver: 接收到广播消息：我是一个普通广播
12-08 17:29:44.280 6644-6644/cn.codingblock.androidadvancestudy I/MyBroadcast5Receiver: 接收到广播消息：我是一个普通广播二、有序广播
在AndroidMainfest.xml中注册广播时通过priority（值越优先级越高）节点为广播添加优先级，然后再用Context.sendOrderedBroadcast()发送，接收者们就会按照优先级顺序依次执行。
有序广播的接收者和给下一个接收者传递数据，并且接收者在收到广播之后可以抛弃广播，使广播不再向后传递。
为上面6个接收器添加优先级：
<receiver android:name=".broadcast.MyBroadcastReceiver">
<intent-filter android:priority="1">
<action android:name="MY_BROADCAST_RECEIVER" />
</intent-filter>
</receiver>
<receiver android:name=".broadcast.MyBroadcast6Receiver">
<intent-filter android:priority="6">
<action android:name="MY_BROADCAST_RECEIVER" />
</intent-filter>
</receiver>
<receiver android:name=".broadcast.MyBroadcast2Receiver">
<intent-filter android:priority="2">
<action android:name="MY_BROADCAST_RECEIVER" />
</intent-filter>
</receiver>
<receiver android:name=".broadcast.MyBroadcast3Receiver">
<intent-filter android:priority="3">
<action android:name="MY_BROADCAST_RECEIVER" />
</intent-filter>
</receiver>
<receiver android:name=".broadcast.MyBroadcast4Receiver">
<intent-filter android:priority="4">
<action android:name="MY_BROADCAST_RECEIVER" />
</intent-filter>
</receiver>
<receiver android:name=".broadcast.MyBroadcast5Receiver">
<intent-filter android:priority="5">
<action android:name="MY_BROADCAST_RECEIVER" />
</intent-filter>
</receiver>然后通过sendOrderedBroadcast发送广播观察log：
intent = new Intent(MyBroadcastReceiver.ACTION);
intent.putExtra(INTENT_INFO, "我是一个有序广播");
sendOrderedBroadcast(intent, null);log如下：
12-08 18:17:26.455 25919-25919/cn.codingblock.androidadvancestudy I/MyBroadcast6Receiver: 接收到广播消息：我是一个有序广播
12-08 18:17:26.462 25919-25919/cn.codingblock.androidadvancestudy I/MyBroadcast5Receiver: 接收到广播消息：我是一个有序广播
12-08 18:17:26.464 25919-25919/cn.codingblock.androidadvancestudy I/MyBroadcast4Receiver: 接收到广播消息：我是一个有序广播
12-08 18:17:26.465 25919-25919/cn.codingblock.androidadvancestudy I/MyBroadcast3Receiver: 接收到广播消息：我是一个有序广播
12-08 18:17:26.466 25919-25919/cn.codingblock.androidadvancestudy I/MyBroadcast2Receiver: 接收到广播消息：我是一个有序广播
12-08 18:17:26.467 25919-25919/cn.codingblock.androidadvancestudy I/MyBroadcastReceiver: 接收到广播消息：我是一个有序广播- abortBroadcast()抛弃广播：
普通的广播是没有办法抛弃的，否则会抛出RuntimeException的异常。
只有有序广播才可以通过此方法抛弃。我们在MyBroadcast6Receiver中添加abortBroadcast()方法：
public class MyBroadcast6Receiver extends BroadcastReceiver {
String TAG = MyBroadcast6Receiver.class.getSimpleName();
public static final String ACTION = "MY_BROADCAST_RECEIVER";
@Override
public void onReceive(Context context, Intent intent) {
Log.i(TAG, "接收到广播消息：" + intent.getStringExtra(BroadcastTestActivity.INTENT_INFO));
abortBroadcast();
Log.i(TAG, "丢弃广播");
}
}然后点击发送有序广播，log如下：
12-08 18:34:27.989 1329-1329/cn.codingblock.androidadvancestudy I/MyBroadcast6Receiver: 接收到广播消息：我是一个有序广播
12-08 18:34:27.989 1329-1329/cn.codingblock.androidadvancestudy I/MyBroadcast6Receiver: 丢弃广播可以看到广播已经被丢弃了。
- setResult()传递给下一个接收者结果。
- getResult()接收上一个接收者的结果。
在MyBroadcast6Receiver中添加setResult方法，在MyBroadcast5Receiver添加getResult方法：
public class MyBroadcast6Receiver extends BroadcastReceiver {
String TAG = MyBroadcast6Receiver.class.getSimpleName();
public static final String ACTION = "MY_BROADCAST_RECEIVER";
@Override
public void onReceive(Context context, Intent intent) {
Log.i(TAG, "接收到广播消息：" + intent.getStringExtra(BroadcastTestActivity.INTENT_INFO));
// abortBroadcast();
// Log.i(TAG, "丢弃广播");
setResult(006, "我是老6传来的消息", null);
}
}
public class MyBroadcast5Receiver extends BroadcastReceiver {
String TAG = MyBroadcast5Receiver.class.getSimpleName();
public static final String ACTION = "MY_BROADCAST_RECEIVER";
@Override
public void onReceive(Context context, Intent intent) {
Log.i(TAG, "接收到广播消息：" + intent.getStringExtra(BroadcastTestActivity.INTENT_INFO));
String data = getResultData();
Log.i(TAG, "data=" + data);
}
}log如下：
12-08 18:40:01.415 10372-10372/cn.codingblock.androidadvancestudy I/MyBroadcast6Receiver: 接收到广播消息：我是一个有序广播
12-08 18:40:01.434 10372-10372/cn.codingblock.androidadvancestudy I/MyBroadcast5Receiver: 接收到广播消息：我是一个有序广播
12-08 18:40:01.434 10372-10372/cn.codingblock.androidadvancestudy I/MyBroadcast5Receiver: data=我是老6传来的消息
12-08 18:40:01.440 10372-10372/cn.codingblock.androidadvancestudy I/MyBroadcast4Receiver: 接收到广播消息：我是一个有序广播
12-08 18:40:01.442 10372-10372/cn.codingblock.androidadvancestudy I/MyBroadcast3Receiver: 接收到广播消息：我是一个有序广播
12-08 18:40:01.445 10372-10372/cn.codingblock.androidadvancestudy I/MyBroadcast2Receiver: 接收到广播消息：我是一个有序广播
12-08 18:40:01.447 10372-10372/cn.codingblock.androidadvancestudy I/MyBroadcastReceiver: 接收到广播消息：我是一个有序广播三、本地广播
以上的广播对于系统来说是全局的，发出广播后，系统内的应用只要注册了相应的接收器就都可以收到广播。如果我们想在本应用发出的广播只在此应用内可以收到，那么可以使用本地广播了。
本地广播由 LocalBroadcastManager 管理，是在 API 21 以后添加的，使用起来也很方便，需要先通过 LocalBroadcastManager.getInstance() 方法获取其单例，剩下的用法与其他广播类似，其主要方法有以下几个：
- registerReceiver():注册广播接收器。
- unregisterReceiver():解除广播接收器。
- sendBroadcast():发送异步广播。
- sendBroadcastSync():发送同步广播。
使用本地广播时，无需在AndroidMainfest.xml中注册，必须使用 LocalBroadcastManager.getInstance(...).registerReceiver(..)来注册接收器。
我们来写个本地广播的小栗子，首先注册两个本地广播：
LocalBroadcastManager.getInstance(context).registerReceiver(new MyBroadcastReceiver(), new IntentFilter(MyBroadcastReceiver.ACTION));
LocalBroadcastManager.getInstance(context).registerReceiver(new MyBroadcast2Receiver(), new IntentFilter(MyBroadcastReceiver.ACTION));然后发送本地广播：
intent.putExtra(INTENT_INFO, "我是一个本地广播");
LocalBroadcastManager.getInstance(context).sendBroadcast(intent);log如下：
12-09 17:20:47.799 15019-15019/cn.codingblock.androidadvancestudy I/MyBroadcastReceiver: 接收到广播消息：我是一个本地广播
12-09 17:20:47.799 15019-15019/cn.codingblock.androidadvancestudy I/MyBroadcast2Receiver: 接收到广播消息：我是一个本地广播四、sticky广播（不建议使用）
sticky广播会一直处于滞留状态，sticky广播被发出后，只要有能够匹配其的新接收器被注册了就可以收到广播，sticky广播通过Context.sendStickyBroadcast()发送。
最后想说的是，本系列文章为博主对Android知识进行再次梳理，查缺补漏的学习过程，一方面是对自己遗忘的东西加以复习重新掌握，另一方面相信在重新学习的过程中定会有巨大的新收获，如果你也有跟我同样的想法，不妨关注我一起学习，互相探讨，共同进步！
参考文献：
- 《Android开发艺术探索》
- 《Android开发进阶从小工到专家》
