Android Messenger的使用（配源码）

零、完整源代码

链接: https://github.com/jx0260/TestGradle

一、写服务端

public class MessengerService extends Service {

    private String TAG = "MessengerService";

    private Handler mHandler = new Handler(Looper.getMainLooper()) {
        @Override
        public void handleMessage(@NonNull Message msg) {
            super.handleMessage(msg);

            Bundle data = msg.getData();
            if (data.getInt("code") == 1) {
                String objStr = data.getString("obj");
                Log.i(TAG, "Server: receive " + objStr + " - is blue!");

                Messenger clientMsger = msg.replyTo;
                if (clientMsger != null) {
                    Message receiptMsg = new Message();
                    Bundle bundle = new Bundle();
                    bundle.putString("cont", "I'm server, I received: sky is blue.");
                    receiptMsg.setData(bundle);

                    try {
                        Log.i(TAG, "Server send back received msg.");
                        clientMsger.send(receiptMsg);
                    } catch (RemoteException e) {
                        e.printStackTrace();
                    }
                }
            }
        }
    };

    @Nullable
    @Override
    public IBinder onBind(Intent intent) {
        return new Messenger(mHandler).getBinder();
    }
}
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创建一个Service，MessengerService，声明 private Handler mHandler = new Handler 一个成员变量，此Handler用于处理来自客户端的请求。
在 onBind() 方法中，创建一个Messenger 对象（指定Handler）并返回给客户端。
配一下manifest.xml ( 注意 android:exported=“true”)

<service
    android:name=".MessengerService"
    android:enabled="true"
    android:exported="true">
    <intent-filter>
        <action android:name="com.example.testgradle.MessengerService"/>
    </intent-filter>
</service>
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二、写客户端

private Messenger mClientMessenger;

@Override
protected void onCreate(@Nullable Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
	Intent messengerIntent = new Intent("com.example.testgradle.MessengerService");
	messengerIntent.setPackage("com.example.testgradle");
	bindService(messengerIntent, new ServiceConnection() {
	    @Override
	    public void onServiceConnected(ComponentName name, IBinder service) {
	        mClientMessenger = new Messenger(service);
	        sendMessageToServer();
	    }
	
	    @Override
	    public void onServiceDisconnected(ComponentName name) {
	
	    }
	}, BIND_AUTO_CREATE);
	
	findViewById(R.id.btn_send_msg_to_server).setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            sendMessageToServer();
        }
    });
}

private void sendMessageToServer() {
    Log.i(TAG, "send msg to server...(sky)");
    Message msg = Message.obtain();
    Bundle bundle = new Bundle();
    bundle.putString("obj", "sky");
    bundle.putInt("code", 1);
    msg.setData(bundle);

    Log.i(TAG, "pass the client's Messenger to Server!");
    msg.replyTo = new Messenger(mReceiveHandler);

    try {
        mClientMessenger.send(msg);
    } catch (RemoteException e) {
        e.printStackTrace();
    }
}
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在 onServiceConnected () 回调中，将IBinder 对象，重新封装成 Messenger。
在 sendMessageToServer() 方法中，构造 Message 传入数据，通过 mClientMessenger 发送出去。
注：此处构造的 Message msg = Message.obtain(); 在封装数据时，必须使用 Bundle，跨进程通信底层用的是 Parcelable 接口，而Bundle的实现如下：

public final class Bundle implements Parcelable
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如果不使用Bundle，会报空Parcelable 的异常。

三、运行 客户端发到服务端进行处理

打印日志：

com.example.clientdemo I/ClientActivity: send msg to server...(sky)
com.example.clientdemo I/ClientActivity: pass the client's Messenger to Server!
com.example.testgradle I/MessengerService: Server: receive sky - is blue!
com.example.testgradle I/MessengerService: Server send back received msg.
com.example.clientdemo I/ClientActivity: Client received:I'm server, I received: sky is blue.
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四、服务端给客户端 回传数据

4.1客户端处理

Log.i(TAG, "pass the client's Messenger to Server!");
msg.replyTo = new Messenger(mReceiveHandler);
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我们在构造往服务端发送的Message时，向其中设置了一个 replyTo，其值为 new 一个Messenger，指定了一个在客户端创建的 mReceiveHandler 用来处理从服务端传来的消息：

private Handler mReceiveHandler = new Handler(Looper.getMainLooper()) {
    @Override
    public void handleMessage(@NonNull Message msg) {
        super.handleMessage(msg);

        Bundle data = msg.getData();
        String cont = data.getString("cont");
        Log.i(TAG, "Client received:" + cont);
    }
};
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简单说就是把一个客户端的 Messenger 传到了服务端，服务端使用此对象，向客户端回发数据。

4.2 服务端处理

Messenger clientMsger = msg.replyTo;
if (clientMsger != null) {
    Message receiptMsg = new Message();
    Bundle bundle = new Bundle();
    bundle.putString("cont", "I'm server, I received: sky is blue.");
    receiptMsg.setData(bundle);

    try {
        Log.i(TAG, "Server send back received msg.");
        clientMsger.send(receiptMsg);
    } catch (RemoteException e) {
        e.printStackTrace();
    }
}
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注意，往客户端回发时，一样要使用Bundle。