Android Messenger realizes two way communication between processes
- 2021-12-13 09:08:01
- OfStack
Brief introduction
Messenger is the simplest way of Android inter-process communication (IPC), which can realize two-way communication between processes. See official website for details
Code implementation
Server application implementation
MessengerService receives messages from clients:
package com.test.messengerservice;
import android.app.Service;
import android.content.Intent;
import android.os.Handler;
import android.os.IBinder;
import android.os.Message;
import android.os.Messenger;
import android.os.RemoteException;
import android.util.Log;
import androidx.annotation.NonNull;
public class MessengerService extends Service {
// Message type of receiving client
private static final int SEND_MESSENGER = 0;
private static final int CONFIG_NET = 1;
private static final int CANCEL = 2;
// Type of message sent to client
private static final int FIND_DEVICE = 10;
public MessengerService() {
}
private Messenger messenger = new Messenger(new ServiceHandler());
private static Messenger mClient;
public class ServiceHandler extends Handler {
@Override
public void handleMessage(@NonNull Message msg) {
// Processing messages
switch(msg.what){
case SEND_MESSENGER:
Log.d("service", "receive messenger");
mClient = msg.replyTo;
break;
case CONFIG_NET:
Log.d("service", "config net task");
mClient = msg.replyTo;
break;
case CANCEL:
Log.d("service", "cancel task");
mClient = msg.replyTo;
break;
default:
break;
}
}
}
@Override
public IBinder onBind(Intent intent) {
Log.i("service", "service bind");
return messenger.getBinder();
}
@Override
public boolean onUnbind(Intent intent) {
Log.i("service", "service unbind");
mClient = null;
return super.onUnbind(intent);
}
// Send a message to the client
public static void sendMessage() {
if (null == mClient) {
Log.d("service", "client is null");
return;
}
try {
Message message = Message.obtain(null, FIND_DEVICE);
mClient.send(message);
} catch (RemoteException e) {
e.printStackTrace();
}
}
}
Register the messenger service in AndroidManifest. xml:
<service
android:name=".MessengerService"
android:enabled="true"
android:exported="true">
<intent-filter>
<action android:name="android.intent.action.MESSENGER"/>
</intent-filter>
</service>
The setup buttons in MainActivity are used to actively send messages to the client:
package com.test.messengerservice;
import androidx.appcompat.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
public class MainActivity extends AppCompatActivity {
private Button button;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
button = findViewById(R.id.findDeviceButton);
button.setOnClickListener( new View.OnClickListener() {
@Override
public void onClick(View v) {
MessengerService.sendMessage();
}
});
}
}
Client application implementation
Bind the server's service in MainActivity and set the button to send messages to the client:
package com.test.messengerclient;
import androidx.annotation.NonNull;
import androidx.appcompat.app.AppCompatActivity;
import android.content.ComponentName;
import android.content.Context;
import android.content.Intent;
import android.content.ServiceConnection;
import android.os.Bundle;
import android.os.Handler;
import android.os.IBinder;
import android.os.Message;
import android.os.Messenger;
import android.os.RemoteException;
import android.util.Log;
import android.view.View;
import android.widget.Button;
public class MainActivity extends AppCompatActivity {
// Server-side Messenger
private Messenger mService;
// Client's Messenger
private Messenger mMessenger;
private Button buttonConfigNet;
private Button buttonCancel;
// Type of message sent to server
private static final int SEND_MESSENGER = 0;
private static final int CONFIG_NET = 1;
private static final int CANCEL = 2;
// Receive the message type of the server
private static final int FIND_DEVICE = 10;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
// Client Messenger
mMessenger = new Messenger(new ClientHandler());
// Binding service
bindServiceInvoked();
// Set click events
buttonConfigNet = findViewById(R.id.buttonConfigNet);
buttonCancel = findViewById(R.id.buttonCancel);
buttonConfigNet.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
if(mService != null) {
try {
Log.d("client", "send config net");
Message message = Message.obtain(null, CONFIG_NET);
message.replyTo = mMessenger;
mService.send(message);
} catch (RemoteException e) {
e.printStackTrace();
}
}
}
});
buttonCancel.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
if(mService != null) {
try {
Log.d("client", "send cancel");
Message message = Message.obtain(null, CANCEL);
message.replyTo = mMessenger;
mService.send(message);
} catch (RemoteException e) {
e.printStackTrace();
}
}
}
});
}
// Receive service connection and disconnection messages
ServiceConnection serviceConnection = new ServiceConnection() {
@Override
public void onServiceConnected(ComponentName name, IBinder service) {
Log.i("client", "service connected");
mService = new Messenger(service);
// Because the server does not have the client's after binding Messenger After binding, put the client first Messenger Send to the server
if(mService != null) {
try {
Log.d("client", "send messenger");
Message message = Message.obtain(null, SEND_MESSENGER);
message.replyTo = mMessenger;
mService.send(message);
} catch (RemoteException e) {
e.printStackTrace();
}
}
}
@Override
public void onServiceDisconnected(ComponentName name) {
Log.i("client", "service disconnected");
mService = null;
}
};
// Receive messages from the server
public class ClientHandler extends Handler {
@Override
public void handleMessage(@NonNull Message msg) {
switch (msg.what){
case FIND_DEVICE:
Log.i("client", "find device");
break;
}
}
}
// Bind server-side service
private void bindServiceInvoked()
{
Intent intent = new Intent();
intent.setAction("android.intent.action.MESSENGER");
intent.setPackage("com.test.messengerservice");
bindService(intent, serviceConnection, Context.BIND_AUTO_CREATE);
}
}