Android 应用开发<二> Broadcast

Android Broadcast

Android 广播

标准广播：发出一条广播后，几乎所有的接受器都会在同一时刻接受。这种广播的接受效率更高，但是缺点就是无法被截断

有序广播：广播发出后，同一时刻只有一个广播接收器可以接受，只有在该接收器接收完成后，才能继续传递。优先级高的先接收到，并可以进行拦截。

接收系统广播

Android 内置了许多系统广播，比如开机、电量变化、时间变化等等。广播接收器可以自由地对自己感兴趣的广播进行注册。注册方式分为：在代码中注册（动态注册）和在AndroidManifest.xml(静态注册)

动态注册

    private IntentFilter intentFilter;
    private NetworkChangeReceiver networkChangeReceiver;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
    ....
        intentFilter = new IntentFilter();
        intentFilter.addAction("android.net.conn.CONNECT_CHANGE");
        networkChangeReceiver = new NetworkChangeReceiver();
        //注册
        registerReceiver(networkChangeReceiver,intentFilter);
    ....
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        unregisterReceiver(networkChangeReceiver);
    }
    //实现 NetworkChangeReceiver
    class NetworkChangeReceiver extends BroadcastReceiver{
        @Override
        public void onReceive(Context context, Intent intent) {
            Toast.makeText(context,"network change",Toast.LENGTH_SHORT).show();
        }

静态注册

动态注册可以很自由控制注册与注销，相对较为灵活，但是因为注册程序是放在onCreate函数中做的，所以必须运行了 app 后才可以进行接收

<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.hooltech.broastcasttest">

    <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
    <!-- 添加相关的权限 -->
    <uses-permission android:name="android.permission.RECEIVE_BOOT_COMPLETED" />

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">

        <receiver
            android:name=".BootCompleteReceiver"
            android:enabled="true"
            android:exported="true">
            <!-- 添加开机监听广播 -->
            <intent-filter>
                <action android:name="android.intent.action.BOOT_COMPLETED" />
            </intent-filter>
        </receiver>
    </application>

</manifest>

接收部分代码

public class BootCompleteReceiver extends BroadcastReceiver {

    @Override
    public void onReceive(Context context, Intent intent) {
        // TODO: This method is called when the BroadcastReceiver is receiving
        // an Intent broadcast.
        Toast.makeText(context,"Boot Complete",Toast.LENGTH_LONG).show();
    }
}

自定义广播

上面说的都是Android系统自带的广播，下面来自己实现自定义广播

标准广播

核心函数为 sendBroadcast 函数

Intent intent = new Intent("com.example.broadcasttest.MY_BROADCAST");
sendBroadcast(intent);

广播接收部分就和之前的一致了

有序广播

核心函数为 sendOrderedBroadcast

Intent intent = new Intent("com.example.broadcasttest.MY_BROADCAST");
sendBroadcast(intent);

注意在AndroidManifest.xml 中，需要添加优先级

            <intent-filter android:priority="100">
                <action android:name="com.example.broadcasttest.MY_BROADCAST" />
            </intent-filter>

接受部分代码,添加 abortBroadcast 用于截断该条广播

public class BootCompleteReceiver extends BroadcastReceiver {

    @Override
    public void onReceive(Context context, Intent intent) {
        // TODO: This method is called when the BroadcastReceiver is receiving
        // an Intent broadcast.
        Toast.makeText(context,"Boot Complete",Toast.LENGTH_LONG).show();
        abortBroadcast();
    }
}

本地广播

上面讨论的自定义广播还有一个问题，广播发送是全局发送的，这样就容易产生安全性问题，所以我们也可以实现本地广播。关键类LocalBroadcastManager

private LocalReceiver localReceiver;
private LocalBroadcastManager localBroadcastManager;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
    localBroadcastManager = LocalBroadcastManager.getInstance(this);
    ...
    intentFilter = new IntentFilter();
    intentFilter.addAction("com.example.broadcasttest.LOCAL_BROADCAST");
    localReceiver = new LocalReceiver();
    localBroadcastManager.registerReceiver(localReceiver,intentFilter);
    }
    
    public class localReceiver extends BroadcastReceiver {

    @Override
    public void onReceive(Context context, Intent intent) {
        // TODO: This method is called when the BroadcastReceiver is receiving
        // an Intent broadcast.
        Toast.makeText(context,"Boot Complete",Toast.LENGTH_LONG).show();
    }
}

ctwillson