广播学习

广播的类型

• 标准广播（Normal Broadcasts）--- 异步执行的广播，所有接收器几乎同时收到，效率较高但无法截断
• 有序广播（Ordered Broadcasts）--- 同步执行的广播，接收器一个个地接到广播，一个接收器的逻辑执行完后才会传到下一个接收器，过程可截断

注册广播接收器

1.动态注册----在代码中注册接收器，仅当应用启动时可以收到广播

Sample Code

public class ReceiverTestActivity extends AppCompatActivity {
    private NetworkChangeReceiver mReceiver;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_receiver_test);
        initReceiver();
    }

    private void initReceiver() {
        IntentFilter filter = new IntentFilter();
        filter.addAction("android.net.conn.CONNECTIVITY_CHANGE");
        mReceiver = new NetworkChangeReceiver();
        registerReceiver(mReceiver, filter);
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        if(mReceiver != null){
            unregisterReceiver(mReceiver);
        }
    }

    class NetworkChangeReceiver extends BroadcastReceiver {

        @Override
        public void onReceive(Context context, Intent intent) {
            //TODO
        }
    }

    public static Intent formatIntent(Context originActivity){
        return new Intent(originActivity, ReceiverTestActivity.class);
    }
}

2.静态注册---- 在Manifest中注册，可以在不运行的时候也接到广播，并处理相应逻辑

发送自定义广播

Sample Code

1. 发送标准广播

    //you should register a custom broadcast receiver in order to handle this broadcast
    private void emmitCustomBroadcast(){
        // String param is your custom intent action
        Intent intent = new Intent("com.example.crane.myfirstline.action.custom_broadcast");
        sendBroadcast(intent);
    }

2.发送有序广播

    //you should register a custom broadcast receiver in order to handle this broadcast
    private void emmitOrderedCustomBroadcast(){
        // String param is your custom intent action, 
        Intent intent = new Intent("com.example.crane.myfirstline.action.custom_broadcast");
        
        //String param is your permission set for this broadcast, it's nullable
        sendOrderedBroadcast(intent, null);
    }

3.阻断有序广播

在广播接收器中onReceive()方法中逻辑末尾添加abortBroadcast()方法

4.使用本地广播

本地广播可以保证该广播只在应用内被接收，防止外部利用广播侵入应用;
使用LocalBroadcastManager的实例中的sendBroadcast(Intent intent)方法
Sample Code

    private void emmitLocalBroadcast() {
        //get Instance of LocalBroadcastManager
        LocalBroadcastManager localBroadcastManager = LocalBroadcastManager.getInstance(this);
        Intent intent = new Intent("com.example.crane.myfirstline.action.local_broadcast");
        localBroadcastManager.sendBroadcast(intent);
    }

作业

利用广播实现强制下线功能