Android四大组件——BroadcastReceiver

1广播的分类

标准广播：完全异步的广播，一旦发出后，所有监听它的广播都会在同一时间收到该信息。
有序广播：同步执行的广播，优先级高的接收器会先收到消息，并且可被截断。

2广播的注册与接收

动态注册

public class MainActivity extends AppCompatActivity {
    private IntentFilter intentFilter;
    private MyReceiver receiver;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        intentFilter = new IntentFilter();
        receiver = new MyReceiver();
        intentFilter.addAction("android.net.conn.CONNECTIVITY_CHANGE");
        registerReceiver(receiver, intentFilter);
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        //动态注册的广播要在onDestroy()方法中取消注册
        unregisterReceiver(receiver);
    }
}

广播接收器类

public class MyReceiver extends BroadcastReceiver {

    @Override
    public void onReceive(Context context, Intent intent) {
        Toast.makeText(context, "network changes", Toast.LENGTH_SHORT).show();
    }
}

GIF.gif

静态注册

在<receiver>标签下通过<intent-filter>标签添加<action>标签来实现

        <receiver
            android:name=".MyReceiver"
            android:enabled="true"
            android:exported="true">
            <intent-filter>
                <!--开机监听-->
                <action android:name="android.intent.action.BOOT_COMPLETED" />
            </intent-filter>
        </receiver>

注意相应权限的添加

发送自定义广播

标准广播

        <receiver
            android:name=".MyBroadcastReceiver"
            android:enabled="true"
            android:exported="true">
            <intent-filter>
                <action android:name="com.example.shaw.myapplication.MyBroadcastReceiver"/>
            </intent-filter>
        </receiver>

       button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Intent intent = new
                        Intent("com.example.shaw.myapplication.MyBroadcastReceiver");
                sendBroadcast(intent);
            }
        });

GIF.gif

有序广播

        <receiver
            android:name=".OrderBroadcastReceiver"
            android:enabled="true"
            android:exported="true">
            <intent-filter android:priority="100"> <!-- 设置接收器的优先级 -->
                <action android:name="com.example.shaw.myapplication.OrderBroadcastReceiver" />
            </intent-filter>
        </receiver>
        <receiver
            android:name=".OrderBroadcastReceiver2"
            android:enabled="true"
            android:exported="true">
            <intent-filter>
                <action android:name="com.example.shaw.myapplication.OrderBroadcastReceiver" />
            </intent-filter>
        </receiver>

有序广播的发送

        button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Intent intent = new
                        Intent("com.example.shaw.myapplication.OrderBroadcastReceiver");
                //第二个参数为与权限相关的字符串，null表示所有接收器都可以接收
                sendOrderedBroadcast(intent,null);
            }
        });

广播接收器1

public class OrderBroadcastReceiver extends BroadcastReceiver {

    @Override
    public void onReceive(Context context, Intent intent) {
        Log.i("OrderBroadcastReceiver", "OrderBroadcastReceiver in received");
        //截断广播
        abortBroadcast();
    }
}

广播接收器2

public class OrderBroadcastReceiver2 extends BroadcastReceiver {

    @Override
    public void onReceive(Context context, Intent intent) {
        Log.i("OrderBroadcastReceiver", "OrderBroadcastReceiver2 in received");
    }
}

运行结果为

图片.png

从Log打印日志可看出广播接收器2没有接受到广播，也就说明了广播被接收器1截断了

本地广播

产生原因：系统全局广播因为可能被其他数据截断造成数据泄露，其他程序也可能向我们的广播接收器发送垃圾广播。
本地广播只能在程序内部进行传递。

        localBroadcastManager = LocalBroadcastManager.getInstance(this);
        button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Intent intent = new Intent("com.example.shaw.myapplication.LOCAL_BROADCAST");
                //使用LocalBroadcastManager实例发送本地广播
                localBroadcastManager.sendBroadcast(intent);
            }
        });
        intentFilter = new IntentFilter();
        intentFilter.addAction("com.example.shaw.myapplication.LOCAL_BROADCAST");
        //注册本地广播监听器
        localBroadcastManager.registerReceiver(localReceiver, intentFilter);
        registerReceiver(localReceiver2, intentFilter);
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        //使用LocalBroadcastManager实例取消注册
        localBroadcastManager.unregisterReceiver(localReceiver);
        unregisterReceiver(localReceiver2);
    }

public class LocalReceiver extends BroadcastReceiver {

    @Override
    public void onReceive(Context context, Intent intent) {
        Log.d("LocalReceiver", "LocalReceiver received");
    }
}

public class LocalReceiver2 extends BroadcastReceiver {

    @Override
    public void onReceive(Context context, Intent intent) {
        Log.d("LocalReceiver", "LocalReceiver2 received");
    }
}