Android學習筆記（十一）BroadcastReceiver動態注冊、注銷示例

　　在上一篇博文中簡單介紹了一下BroadcastReceiver的相關知識點，本篇舉一個在代碼中動態的注冊、注銷BroadcastReceiver的栗子。

1、首先創建一個MyReceiver並繼承BroadcastReceiver，既然要動態注冊該receiver的話，就無需在AndroidManifest.xml中配置它了：

public class MyReceiver extends BroadcastReceiver {
    public static final String ACTION = "com.codingblock.receive.intent.action.MyReceiver";

    public MyReceiver() {
        
    }

    @Override
    public void onReceive(Context context, Intent intent) {
        System.out.println("接收到的消息為：" + intent.getStringExtra("data"));
    }
}

代碼分析：上面代碼中定義了一個靜態變量ACTION，以方便程序指定該receiver。另外，從onReceive()方法的第二個參數intent可以獲取到傳遞過來的數據。

2、布局文件如下，很簡單，只有三個按鈕：發送消息按鈕、注冊receiver按鈕和注銷receiver按鈕。

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical" >

    <Button
        android:id="@+id/btn_send_receiver"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="發送消息" />
    
    <Button
        android:id="@+id/btn_register_receiver"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="注冊receiver" />
    
    <Button
        android:id="@+id/btn_unregister_receiver"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="注銷receiver" />

</LinearLayout>

3、最后在MainActivity中測試一下

public class MainActivity extends Activity implements OnClickListener {
    private MyReceiver receiver = null;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        findViewById(R.id.btn_send_receiver).setOnClickListener(this);
        findViewById(R.id.btn_register_receiver).setOnClickListener(this);
        findViewById(R.id.btn_unregister_receiver).setOnClickListener(this);
    }

    @Override
    public void onClick(View v) {
        switch (v.getId()) {
        case R.id.btn_send_receiver:
            Intent i = new Intent(MyReceiver.ACTION);
            i.putExtra("data", "來自MainActivity的消息");
            sendBroadcast(i);
            break;
        case R.id.btn_register_receiver:
            if (receiver == null) {
                System.out.println("注冊receiver");
                receiver = new MyReceiver();
                registerReceiver(receiver, new IntentFilter(MyReceiver.ACTION));
            }
            break;
        case R.id.btn_unregister_receiver:
            if (receiver != null) {
                System.out.println("注銷receiver");
                unregisterReceiver(receiver);
                receiver = null;
            }
            break;

        default:
            break;
        }
    }
}

代碼分析：本段代碼在23行，通過registerReceiver()方法動態的注冊了MyReceiver，並且使用過后最好不要忘了用unregisterReceiver()方法再將其注銷，注銷后應將receiver設為null。

4、運行結果如下

測試就會發現在點擊發送消息按鈕之前，如果沒有注冊receiver的話是不能成功發送消息的，只有注冊了receiver，點擊發送消息log中才有輸出：

從日志輸出就能看出，當注冊好了receiver后，按下發送消息按鈕，在MyReceiver中就能收到來自MainActivity的消息。