Android查缺補漏--BroadcastReceiver的類型與使用

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Broadcast 是一種被用於應用內和應用之間傳遞資訊的機制。一個廣播可以對應多個接受者。一個完整的廣播機制，需要具有以下三個要素：

• 發送廣播的Broadcast
• 接受廣播的BroadcastReceiver
• 傳遞資訊的Intent

廣播的註冊分為靜態註冊和動態註冊：

• 靜態註冊：靜態註冊的廣播是指在AndroidManifest中註冊的廣播，此種廣播在應用安裝時就被系統解析，不需要啟動應用就可以收到相應的廣播。

<receiver android:name=".broadcast.MyBroadcastReceiver">    <intent-filter>        <action android:name="MY_BROADCAST_RECEIVER" />    </intent-filter></receiver>

• 動態註冊：通過Context.registerReceiver()來實現，不需要時要通過Context.unRegisterReceiver()解除廣播，此種廣播必須應用啟動後才能註冊並接收廣播。

  // 動態註冊廣播接收器registerReceiver(new DynamicBroadcastReceiver(), new IntentFilter(MyBroadcastReceiver.ACTION));

廣播又分為普通廣播、有序廣播、本地廣播和sticky廣播。

一、普通廣播

普通廣播通過Context.sendBroadcast()發送，我們沒有辦法制定Receiver們對於普通廣播的接收順序。理論上所有的接收器（Receiver）接收到廣播的順序不確定，但一般是按照其在AndroidMainfest.xml檔案中註冊的順序（不絕對）。
普通廣播中，接受者不能將處理結果傳遞給下一個接收器，也無法終止廣播的傳播。

如下代碼是一個靜態註冊的廣播樣本：

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, "接收到廣播訊息：" + intent.getStringExtra(BroadcastTestActivity.INTENT_INFO));    }}

然後再AndroidMainfest.xml中註冊這個廣播:

<receiver android:name=".broadcast.MyBroadcastReceiver">    <intent-filter>        <action android:name="MY_BROADCAST_RECEIVER" />    </intent-filter></receiver>

接下來在Activity中調用Context.sendBroadcast()發送廣播就可以了：

Intent intent = new Intent(MyBroadcastReceiver.ACTION);intent.putExtra(INTENT_INFO, "我是一個普通廣播");sendBroadcast(intent);

log如下：

12-08 17:29:44.259 6644-6644/cn.codingblock.androidadvancestudy I/MyBroadcastReceiver: 接收到廣播訊息：我是一個普通廣播

• 普通廣播的接收已排序的測試
  我們仿照MyBroadcastReciver建立多個接收器，代碼一樣：

/** * 靜態註冊的廣播接收器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, "接收到廣播訊息：" + intent.getStringExtra(BroadcastTestActivity.INTENT_INFO));    }}/** * 靜態註冊的廣播接收器3 * Created by liuwei on 17/12/7. */public class MyBroadcast3Receiver extends BroadcastReceiver {...}/** * 靜態註冊的廣播接收器4 * Created by liuwei on 17/12/7. */public class MyBroadcast4Receiver extends BroadcastReceiver {...}/** * 靜態註冊的廣播接收器5 * Created by liuwei on 17/12/7. */public class MyBroadcast5Receiver extends BroadcastReceiver {...}/** * 靜態註冊的廣播接收器6 * Created by liuwei on 17/12/7. */public class MyBroadcast6Receiver extends BroadcastReceiver {...}

然後在AndroidMainfest.xml中為以上廣播都註冊同一個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>

點擊發送廣播，查看log：

12-08 17:29:44.259 6644-6644/cn.codingblock.androidadvancestudy I/MyBroadcastReceiver: 接收到廣播訊息：我是一個普通廣播12-08 17:29:44.268 6644-6644/cn.codingblock.androidadvancestudy I/MyBroadcast6Receiver: 接收到廣播訊息：我是一個普通廣播12-08 17:29:44.271 6644-6644/cn.codingblock.androidadvancestudy I/MyBroadcast2Receiver: 接收到廣播訊息：我是一個普通廣播12-08 17:29:44.273 6644-6644/cn.codingblock.androidadvancestudy I/MyBroadcast3Receiver: 接收到廣播訊息：我是一個普通廣播12-08 17:29:44.277 6644-6644/cn.codingblock.androidadvancestudy I/MyBroadcast4Receiver: 接收到廣播訊息：我是一個普通廣播12-08 17:29:44.280 6644-6644/cn.codingblock.androidadvancestudy I/MyBroadcast5Receiver: 接收到廣播訊息：我是一個普通廣播

二、有序廣播

在AndroidMainfest.xml中註冊廣播時通過priority（值越優先順序越高）節點為廣播添加優先順序，然後再用Context.sendOrderedBroadcast()發送，接收者們就會按照優先順序順序依次執行。

有序廣播的接收者和給下一個接收者傳遞資料，並且接收者在收到廣播之後可以拋棄廣播，使廣播不再向後傳遞。

為上面6個接收器添加優先順序：

<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>

然後通過sendOrderedBroadcast發送廣播觀察log：

intent = new Intent(MyBroadcastReceiver.ACTION);intent.putExtra(INTENT_INFO, "我是一個有序廣播");sendOrderedBroadcast(intent, null);

log如下：

12-08 18:17:26.455 25919-25919/cn.codingblock.androidadvancestudy I/MyBroadcast6Receiver: 接收到廣播訊息：我是一個有序廣播12-08 18:17:26.462 25919-25919/cn.codingblock.androidadvancestudy I/MyBroadcast5Receiver: 接收到廣播訊息：我是一個有序廣播12-08 18:17:26.464 25919-25919/cn.codingblock.androidadvancestudy I/MyBroadcast4Receiver: 接收到廣播訊息：我是一個有序廣播12-08 18:17:26.465 25919-25919/cn.codingblock.androidadvancestudy I/MyBroadcast3Receiver: 接收到廣播訊息：我是一個有序廣播12-08 18:17:26.466 25919-25919/cn.codingblock.androidadvancestudy I/MyBroadcast2Receiver: 接收到廣播訊息：我是一個有序廣播12-08 18:17:26.467 25919-25919/cn.codingblock.androidadvancestudy I/MyBroadcastReceiver: 接收到廣播訊息：我是一個有序廣播

• abortBroadcast()拋棄廣播：
  普通的廣播是沒有辦法拋棄的，否則會拋出RuntimeException的異常。

只有有序廣播才可以通過此方法拋棄。我們在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, "接收到廣播訊息：" + intent.getStringExtra(BroadcastTestActivity.INTENT_INFO));        abortBroadcast();        Log.i(TAG, "丟棄廣播");    }}

然後點擊發送有序廣播，log如下：

12-08 18:34:27.989 1329-1329/cn.codingblock.androidadvancestudy I/MyBroadcast6Receiver: 接收到廣播訊息：我是一個有序廣播12-08 18:34:27.989 1329-1329/cn.codingblock.androidadvancestudy I/MyBroadcast6Receiver: 丟棄廣播

可以看到廣播已經被丟棄了。

• setResult()傳遞給下一個接收者結果。
• getResult()接收上一個接收者的結果。

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, "接收到廣播訊息：" + intent.getStringExtra(BroadcastTestActivity.INTENT_INFO));//        abortBroadcast();//        Log.i(TAG, "丟棄廣播");        setResult(006, "我是老6傳來的訊息", 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, "接收到廣播訊息：" + 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: 接收到廣播訊息：我是一個有序廣播12-08 18:40:01.434 10372-10372/cn.codingblock.androidadvancestudy I/MyBroadcast5Receiver: 接收到廣播訊息：我是一個有序廣播12-08 18:40:01.434 10372-10372/cn.codingblock.androidadvancestudy I/MyBroadcast5Receiver: data=我是老6傳來的訊息12-08 18:40:01.440 10372-10372/cn.codingblock.androidadvancestudy I/MyBroadcast4Receiver: 接收到廣播訊息：我是一個有序廣播12-08 18:40:01.442 10372-10372/cn.codingblock.androidadvancestudy I/MyBroadcast3Receiver: 接收到廣播訊息：我是一個有序廣播12-08 18:40:01.445 10372-10372/cn.codingblock.androidadvancestudy I/MyBroadcast2Receiver: 接收到廣播訊息：我是一個有序廣播12-08 18:40:01.447 10372-10372/cn.codingblock.androidadvancestudy I/MyBroadcastReceiver: 接收到廣播訊息：我是一個有序廣播

三、本地廣播

以上的廣播對於系統來說是全域的，發出廣播後，系統內的應用只要註冊了相應的接收器就都可以收到廣播。如果我們想在本應用發出的廣播只在此應用內可以收到，那麼可以使用本地廣播了。

本地廣播由 LocalBroadcastManager 管理，是在 API 21 以後添加的，使用起來也很方便，需要先通過 LocalBroadcastManager.getInstance() 方法擷取其單例，剩下的用法與其他廣播類似，其主要方法有以下幾個：

• registerReceiver():註冊廣播接收器。
• unregisterReceiver():解除廣播接收器。
• sendBroadcast():發送非同步廣播。
• sendBroadcastSync():發送同步廣播。

使用本地廣播時，無需在AndroidMainfest.xml中註冊，必須使用 LocalBroadcastManager.getInstance(...).registerReceiver(..)來註冊接收器。

我們來寫個本地廣播的小栗子，首先註冊兩個本地廣播：

LocalBroadcastManager.getInstance(context).registerReceiver(new MyBroadcastReceiver(), new IntentFilter(MyBroadcastReceiver.ACTION));LocalBroadcastManager.getInstance(context).registerReceiver(new MyBroadcast2Receiver(), new IntentFilter(MyBroadcastReceiver.ACTION));

然後發送本地廣播：

intent.putExtra(INTENT_INFO, "我是一個本地廣播");LocalBroadcastManager.getInstance(context).sendBroadcast(intent);

log如下：

12-09 17:20:47.799 15019-15019/cn.codingblock.androidadvancestudy I/MyBroadcastReceiver: 接收到廣播訊息：我是一個本地廣播12-09 17:20:47.799 15019-15019/cn.codingblock.androidadvancestudy I/MyBroadcast2Receiver: 接收到廣播訊息：我是一個本地廣播

四、sticky廣播（不建議使用）

sticky廣播會一直處於滯留狀態，sticky廣播被發出後，只要有能夠匹配其的新接收器被註冊了就可以收到廣播，sticky廣播通過Context.sendStickyBroadcast()發送。

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參考文獻：

• 《Android開發藝術探索》
• 《Android開發進階從小工到專家》

Android查缺補漏--BroadcastReceiver的類型與使用