0x00 前言

继续写“第一行代码”的读书笔记，这次看看Android的广播机制

0x01 广播机制

广播机制分为两类：

标准广播：异步的，广播发送之后，所有的广播接收器几乎同时接受广播，广播效率比较高。但不能截断。
有序广播：同步执行的，优先级高的先接受到，之前的广播接收器可以截断广播。

0x02 动态注册广播接收器和静态注册广播接收器

先来看如何写动态注册，关键函数是：registerReceiver(networkChangReceiver,intentFilter)

public class MainActivity extends AppCompatActivity {

    private IntentFilter intentFilter;
    private NetworkChangReceiver networkChangReceiver;

    class NetworkChangReceiver extends BroadcastReceiver {
        @Override
        public void onReceive(Context context,Intent intent) {
            Toast.makeText(context,"Netwokchange",Toast.LENGTH_SHORT).show();
        }

    }

    protected void onDestroy() {
        super.onDestroy();
        unregisterReceiver(networkChangReceiver);//注销广播接收器
    }

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.first_layout);
        Button button1 = (Button) findViewById(R.id.button_1);
        intentFilter = new IntentFilter();
        intentFilter.addAction("android.net.conn.CONNECTIVITY_CHANGE");//定义广播接收器的接收动作
        networkChangReceiver = new NetworkChangReceiver();//新建一个广播接收器
        registerReceiver(networkChangReceiver,intentFilter);//动态注册广播接收器

静态注册的编写方法就简单多了，直接定义一个接收类，

public class MyReceiver 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, "开机 ", Toast.LENGTH_SHORT).show();
        throw new UnsupportedOperationException("Not yet implemented");
    }
}

在AndroidManifest.xml中注册,添加Intentfileter；并且开启权限:RECEIVE_BOOT_COMPLETED

<uses-permission android:name="android.permission.RECEIVE_BOOT_COMPLETED"/>
<receiver
            android:name=".MyReceiver"
            android:enabled="true"
            android:exported="true">
            <intent-filter>
                <action android:name="android.intent.action.BOOT_COMPLETED" />
            </intent-filter>
        </receiver>

0x03 发送广播

发送标准广播

基本步骤为：新建一个广播接收器，在然后AndroidManifest.xml中注册,添加Intentfileter，发送自定义广播，也就是Intent。

这里的广播接收器我用上面的就OK了，只需要添加一个Intentfileter就完成。

//发送标准广播到我们定义的广播接收器
        Button button5 = (Button) findViewById(R.id.button_5);
        button3.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Intent intent=new Intent("com.example.broadcastdemo.MY_BROADCAST");//还是要用到Intent
                sendBroadcast(intent);

发送有序广播

发送广播方式改为：sendOrderedBroadcast(intent, null);


Button button5 = (Button) findViewById(R.id.button_5);
        button3.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Intent intent=new Intent("com.example.broadcastdemo.MY_BROADCAST");
                sendOrderedBroadcast(intent,null);//发送有序广播
            }
        });

广播截断:abortBroadcast();

public class MyReceiver extends BroadcastReceiver {
    //自定义的广播接收器
    @Override
    public void onReceive(Context context, Intent intent) {
        // TODO: This method is called when the BroadcastReceiver is receiving
        // an Intent broadcast.
        Toast.makeText(context, "接收信息成功", Toast.LENGTH_SHORT).show();
        abortBroadcast(); //截断广播
    }
}

本地广播

前面解释的都是全局广播，其他应用程序可以接收，本地广播只能够在应用程序的内部进行传递，有效更加安全性。

@Override
   protected void onCreate(Bundle savedInstanceState) {
       super.onCreate(savedInstanceState);
       setContentView(R.layout.second_layout);
       localBroadcastManager = LocalBroadcastManager.getInstance(this);
       Button button5 = (Button) findViewById(R.id.button_5);
       button5.setOnClickListener(new View.OnClickListener() {
           @Override
           public void onClick(View v) {
               Intent intent=new Intent("com.example.broadcastdemo.MY_BROADCAST_LOCAL");
               //发送本地广播
               localBroadcastManager.sendBroadcast(intent);
           }
       });

静态注册本地广播接收器：localBroadcastManager.registerReceiver(localReceiver,intentFilter);

intentFilter = new IntentFilter();
        //定义广播接收器的接收动作
        intentFilter.addAction("com.example.broadcastdemo.MY_BROADCAST_LOCAL");

        localReceiver = new LocalReceiver();
        //静态注册本地广播接收器
        localBroadcastManager.registerReceiver(localReceiver,intentFilter);