对于不同进程中的Activity和Service，要实现IPC（跨进程通信），其实就是通过IBinder接口，其中可能涉及到AIDL编程，和操作系统提供的进程通信接口这些底层c++知识。然而，Google已经为我们封装了一套Messenger机制，其底层也是使用AIDL实现的。要使用这套机制，必须为通信双方建立各自的Messenger，然后Service的Messenger依然是通过IBinder传递到Activity，Activity也可以将自己的Messenger通过Message的replyTo属性传递到Service。
Messenger使用步骤：
- Service需要实现一个Hanlder，用以处理从客户端收到的消息
- 用该Handler创建一个Messenger对象，Messenger对象内部会引用该Handler对象
- 用创建好的Messenger对象获得一个IBinder实例，并且将该IBinder通过Service的onBind方法返回给各个客户端
- 客户端通过收到的IBinder对象实例化一个Messenger对象，该Messenger内部指向指向Service中的Handler。客户端通过该Messenger对象就可以向Service中的Hanlder发送消息。
- Service中的Hanlder收到消息后，在Handler中的handleMessage方法中处理消息。
- 通过上面的第4步与第5步，就完成了客户端向Service发送消息并且Service接收到消息的单向通信过程，即客户端 -> Service。如果要实现Service向客户端回消息的通信过程，即Service -> 客户端，那么前提是在客户端中也需要像Service一样内部维护有一个指向Handler的Messenger。当在第四步中客户端向Service发送信息时，将Message的replyTo属性设置为客户端自己的Messenger。这样在第5步Service在Handler的handleMessage中处理收到的消息时，可以通过Message的Messenger再向客户端发送Message，这样客户端内维护的Handler对象就会收到来自于Service的Message，从而完成Service向客户端发送消息且客户端接收到消息的通信过程。
综上六步就能完成客户端与Service的跨进程双向通信过程:
客户端 -> Service -> 客户端
为了演示客户端与Service的跨进程通信，我建立了两个应用ClientApp和ServiceApp，两个应用的名称也是见名知意:
- ClientApp, 该App是客户端，用于调用服务
- ServiceApp，该App是Service端，用于供客户端ClientApp调用
注意：跨进程通信使用Bundle，否则会报错Java.lang.RuntimeException: Can’t marshal non-Parcelable objects across processes.
客戶端demo
package com.axaet.servicecommunication;
import android.app.ActivityManager;
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.support.design.widget.FloatingActionButton;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.util.Log;
import android.view.View;
import android.widget.TextView;
import android.widget.Toast;
public class MainActivity extends AppCompatActivity {
private static final String TAG = "yushu";
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
textView = (TextView) findViewById(R.id.text_show);
FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
assert fab != null;
fab.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
Message message = Message.obtain(null, 101);
bundle.putString("key","from MainActivity button");
message.setData(bundle);
message.replyTo = messenger;
try {
mService.send(message);
} catch (RemoteException e) {
e.printStackTrace();
}
}
});
}
String getCurProcessName(Context context) {
int pid = android.os.Process.myPid();
ActivityManager mActivityManager = (ActivityManager) context
.getSystemService(Context.ACTIVITY_SERVICE);
for (ActivityManager.RunningAppProcessInfo appProcess : mActivityManager
.getRunningAppProcesses()) {
if (appProcess.pid == pid) {
return appProcess.processName;
}
}
return null;
}
class MyHandler extends Handler {
@Override
public void handleMessage(Message msg) {
super.handleMessage(msg);
switch (msg.what) {
case 111:
int i = msg.arg1;
if (i == 1) {
Log.i(TAG,"Main="+getCurProcessName(getApplication()));
Bundle bundle=msg.getData();
Toast.makeText(MainActivity.this, "接收到Service消息"+bundle.getString("key"), Toast.LENGTH_SHORT).show();
}
default:
}
}
}
private Bundle bundle = new Bundle();
private Messenger messenger = new Messenger(new MyHandler());
private Messenger mService;
private TextView textView;
private ServiceConnection serviceConnection = new ServiceConnection() {
@Override
public void onServiceConnected(ComponentName name, IBinder service) {
Log.i(TAG, "onServiceConnected: ComponentName = " + name);
mService = new Messenger(service);
textView.setText("连接成功");
Message message = Message.obtain(null, 101);
bundle.putString("key","from MainActivity=11111");
message.setData(bundle);
message.replyTo = messenger;
try {
mService.send(message);
} catch (RemoteException e) {
e.printStackTrace();
}
}
@Override
public void onServiceDisconnected(ComponentName name) {
}
};
@Override
protected void onStart() {
super.onStart();
Intent intent = new Intent();
//參數一為服務端APP包名，參數二為service的完整類名
ComponentName name = new ComponentName("com.axaet.servicecommunication", "com.axaet.servicecommunication.MyService");
intent.setComponent(name); //发送信息
intent.putExtra("data", "msg from MainActivity");
bindService(intent, serviceConnection, BIND_AUTO_CREATE);
}
@Override
protected void onStop() {
super.onStop();
unbindService(serviceConnection);
}
}
服務端demo
package com.axaet.servicecommunication;
import android.annotation.SuppressLint;
import android.app.ActivityManager;
import android.app.Service;
import android.content.Context;
import android.content.Intent;
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 java.util.ArrayList;
import java.util.List;
public class MyService extends Service {
private static final String TAG = "yushu";
public List<String> data = new ArrayList<>();
private Messenger mClient;
@SuppressLint("HandlerLeak")
class MyHandler extends Handler {
@Override
public void handleMessage(Message msg) {
super.handleMessage(msg);
switch (msg.what) {
case 101:
Bundle bundle=msg.getData();
Log.i(TAG,"service="+ bundle.getString("key"));
Log.i(TAG,"service="+getCurProcessName(getApplication()));
Message message = Message.obtain(null, 111, 1, 1);
bundle.putString("key","from service222222");
message.setData(bundle);
mClient = msg.replyTo;
try {
mClient.send(message);
} catch (RemoteException e) {
e.printStackTrace();
}
default:
}
}
}
String getCurProcessName(Context context) {
int pid = android.os.Process.myPid();
ActivityManager mActivityManager = (ActivityManager) context
.getSystemService(Context.ACTIVITY_SERVICE);
for (ActivityManager.RunningAppProcessInfo appProcess : mActivityManager
.getRunningAppProcesses()) {
if (appProcess.pid == pid) {
return appProcess.processName;
}
}
return null;
}
private Messenger messenger = new Messenger(new MyHandler());
public MyService() {
data.add("This is some msg from " + TAG);
}
@Override
public IBinder onBind(Intent intent) {
String s = intent.getStringExtra("data");
Log.i(TAG, "onBind: 接收 " + s);
data.add(s);
return messenger.getBinder();
}
}
参考文章:http://blog.csdn.net/zhou114108/article/details/52050242
