android 多进程下service通讯 Messenger

解决当应用内有多个进程时通讯问题

服务基本上分为两种形式:

    启动
    当应用组件(如 Activity)通过调用 startService() 启动服务时,服务即处于“启动”状态。一旦启动,服务即可在后台无限期运行,即使启动服务的组件已被销毁也不受影响。 已启动的服务通常是执行单一操作,而且不会将结果返回给调用方。例如,它可能通过网络下载或上传文件。 操作完成后,服务会自行停止运行。
    绑定
    当应用组件通过调用 bindService() 绑定到服务时,服务即处于“绑定”状态。绑定服务提供了一个客户端-服务器接口,允许组件与服务进行交互、发送请求、获取结果,甚至是利用进程间通信 (IPC) 跨进程执行这些操作。 仅当与另一个应用组件绑定时,绑定服务才会运行。 多个组件可以同时绑定到该服务,但全部取消绑定后,该服务即会被销毁。

所以 进程间通信需要 bindService();
bindService(Intent service, ServiceConnection conn, int flags)
service 的intent

ServiceConnection用于 服务端(理解远端的service)和本地(当前进程)的连接

flags 是绑定方式 普遍两种 0 或者 Context.BIND_AUTO_CREATE
0 : 绑定service不启动service ,需要手动startService启动service
BIND_AUTO_CREATE : 绑定service后会自动启动service

首先创建一个ServiceConnection,里面两个方法断开和连接的接口

    private ServiceConnection mConnection = new ServiceConnection() {
        public void onServiceConnected(ComponentName className, IBinder service) {
        }

        public void onServiceDisconnected(ComponentName className) {
        }
    };

创建一个服务端service(远端的service)

public class MessengerService extends Service {
    static final String TAG = "MessengerService";
    /**
     * Command to the service to display a message
     */
    static final int MSG_SAY_HELLO = 1;

    /**
     * Handler of incoming messages from clients.
     */
    class IncomingHandler extends Handler {
        @Override
        public void handleMessage(Message msg) {
            switch (msg.what) {
                case MSG_SAY_HELLO:
                    Toast.makeText(getApplicationContext(), "hello!", Toast.LENGTH_SHORT).show();
                    Log.e(TAG, "IncomingHandler-MSG_SAY_HELLO");
                    break;
                default:
                    super.handleMessage(msg);
            }
        }
    }

    /**
     * Target we publish for clients to send messages to IncomingHandler.
     */
    final Messenger mMessenger = new Messenger(new IncomingHandler());

    /**
     * When binding to the service, we return an interface to our messenger
     * for sending messages to the service.
     */
    @Override
    public IBinder onBind(Intent intent) {
        Toast.makeText(getApplicationContext(), "binding", Toast.LENGTH_SHORT).show();
        Log.e(TAG, "onBind");
        return mMessenger.getBinder();
    }
}

xml新起一个进程,

        <service
            android:name=".MessengerService"
            android:enabled="true"
            android:exported="true"
            android:process=":remote"></service>

发起通讯


public class ActivityMessenger extends Activity {
    static final String TAG = "ActivityMessenger";
    /**
     * Messenger for communicating with the service.
     */
    Messenger mService = null;

    /**
     * Flag indicating whether we have called bind on the service.
     */
    boolean mBound;
    /**
     * Class for interacting with the main interface of the service.
     */
    private ServiceConnection mConnection = new ServiceConnection() {
        public void onServiceConnected(ComponentName className, IBinder service) {
            // This is called when the connection with the service has been
            // established, giving us the object we can use to
            // interact with the service.  We are communicating with the
            // service using a Messenger, so here we get a client-side
            // representation of that from the raw IBinder object.
            Log.e(TAG, "ServiceConnection-onServiceConnected");
            mService = new Messenger(service);
            mBound = true;
        }

        public void onServiceDisconnected(ComponentName className) {
            // This is called when the connection with the service has been
            // unexpectedly disconnected -- that is, its process crashed.
            Log.e(TAG, "ServiceConnection-onServiceDisconnected");
            mService = null;
            mBound = false;
        }
    };

    public void sayHello() {
        if (!mBound) return;
        // Create and send a message to the service, using a supported 'what' value
        Message msg = Message.obtain(null, MessengerService.MSG_SAY_HELLO, 0, 0);
        try {
            mService.send(msg);
        } catch (RemoteException e) {
            e.printStackTrace();
        }
    }

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        ((Button) findViewById(R.id.test1)).setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                sayHello();
            }
        });
    }

    @Override
    protected void onStart() {
        super.onStart();
        // Bind to the service
        Intent intent = new Intent(this, MessengerService.class);
        bindService(intent, mConnection, Context.BIND_AUTO_CREATE);

    }

    @Override
    protected void onStop() {
        super.onStop();
        // Unbind from the service
        if (mBound) {
            unbindService(mConnection);
            mBound = false;
        }
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        unbindService(mConnection);
        Toast.makeText(ActivityMessenger.this, "Service Un-Binded", Toast.LENGTH_LONG).show();
    }

}

以上当前进程 就可以和服务端进行通讯了
发送了一条消息MSG_SAY_HELLO ,服务端service弹出hello

现在只是方面发送 而且还无法得到返回消息 .
怎么才能互相通讯呢
需要做一点改变

首先在发送msg时 携带当前service的messenger 并且收到消息后的handle

Handler handler = new Handler(new Handler.Callback() {
        @Override
        public boolean handleMessage(Message msg) {
            switch (msg.what) {
                case MSG_REPLY:
                    Log.e(TAG, "handler-MSG_REPLY");
            }
            return false;
        }
    });

 public void sayHello() {
        Log.e(TAG, "sayHello()");
        if (!mBound) return;
        Message msg = Message.obtain();
        msg.what = MessengerService.MSG_SAY_HELLO;
        msg.replyTo = new Messenger(handler);
        try {
            mService.send(msg);
        } catch (RemoteException e) {
            e.printStackTrace();
        }
    }

服务端需要做的是
根据接收到的message 中的messenger 返回消息
服务端message只有messenger 才知道是哪个service发过来的
messenger理解为信使

    class IncomingHandler extends Handler {
        @Override
        public void handleMessage(Message msg) {
            switch (msg.what) {
                case MSG_SAY_HELLO:
                    Toast.makeText(getApplicationContext(), "hello!", Toast.LENGTH_SHORT).show();
                    Log.e(TAG, "IncomingHandler-MSG_SAY_HELLO");
                    if (msg.replyTo == null) return;

                    Message message = Message.obtain();
                    message.what = ActivityMessenger.MSG_REPLY;
                    Messenger messenger = msg.replyTo;
                    try {
                        messenger.send(message);
                        Log.e(TAG, "IncomingHandler-send-MSG_REPLY");
                    } catch (RemoteException e) {
                        e.printStackTrace();
                    }

                    break;
                default:
                    super.handleMessage(msg);
            }
        }
    }

结果 log


image.png
image.png

两个class 完整code

public class ActivityMessenger extends Activity {
    static final String TAG = "ActivityMessenger";
    static final int MSG_REPLY = 2;
    /**
     * Messenger for communicating with the service.
     */
    Messenger mService = null;

    /**
     * Flag indicating whether we have called bind on the service.
     */
    boolean mBound;
    Handler handler = new Handler(new Handler.Callback() {
        @Override
        public boolean handleMessage(Message msg) {
            switch (msg.what) {
                case MSG_REPLY:
                    Log.e(TAG, "handler-MSG_REPLY");
            }
            return false;
        }
    });
    ;
    /**
     * Class for interacting with the main interface of the service.
     */
    private ServiceConnection mConnection = new ServiceConnection() {
        public void onServiceConnected(ComponentName className, IBinder service) {
            // This is called when the connection with the service has been
            // established, giving us the object we can use to
            // interact with the service.  We are communicating with the
            // service using a Messenger, so here we get a client-side
            // representation of that from the raw IBinder object.
            Log.e(TAG, "ServiceConnection-onServiceConnected");
            mService = new Messenger(service);
            mBound = true;
        }

        public void onServiceDisconnected(ComponentName className) {
            // This is called when the connection with the service has been
            // unexpectedly disconnected -- that is, its process crashed.
            Log.e(TAG, "ServiceConnection-onServiceDisconnected");
            mService = null;
            mBound = false;
        }
    };

    public void sayHello() {
        Log.e(TAG, "sayHello()");
        if (!mBound) return;
        Message msg = Message.obtain();
        msg.what = MessengerService.MSG_SAY_HELLO;
        msg.replyTo = new Messenger(handler);
        try {
            mService.send(msg);
        } catch (RemoteException e) {
            e.printStackTrace();
        }
    }

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        ((Button) findViewById(R.id.test1)).setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                sayHello();
            }
        });
    }

    @Override
    protected void onStart() {
        super.onStart();
        // Bind to the service
        Intent intent = new Intent(this, MessengerService.class);
        bindService(intent, mConnection, Context.BIND_AUTO_CREATE);

    }

    @Override
    protected void onStop() {
        super.onStop();
        // Unbind from the service
        if (mBound) {
            unbindService(mConnection);
            mBound = false;
        }
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        unbindService(mConnection);
        Toast.makeText(ActivityMessenger.this, "Service Un-Binded", Toast.LENGTH_LONG).show();
    }

}

service

public class MessengerService extends Service {
    static final String TAG = "MessengerService";
    /**
     * Command to the service to display a message
     */
    static final int MSG_SAY_HELLO = 1;

    /**
     * Handler of incoming messages from clients.
     */
    class IncomingHandler extends Handler {
        @Override
        public void handleMessage(Message msg) {
            switch (msg.what) {
                case MSG_SAY_HELLO:
                    Toast.makeText(getApplicationContext(), "hello!", Toast.LENGTH_SHORT).show();
                    Log.e(TAG, "IncomingHandler-MSG_SAY_HELLO");
                    if (msg.replyTo == null) return;

                    Message message = Message.obtain();
                    message.what = ActivityMessenger.MSG_REPLY;
                    Messenger messenger = msg.replyTo;
                    try {
                        messenger.send(message);
                        Log.e(TAG, "IncomingHandler-send-MSG_REPLY");
                    } catch (RemoteException e) {
                        e.printStackTrace();
                    }

                    break;
                default:
                    super.handleMessage(msg);
            }
        }
    }

    /**
     * Target we publish for clients to send messages to IncomingHandler.
     */
    final Messenger mMessenger = new Messenger(new IncomingHandler());

    /**
     * When binding to the service, we return an interface to our messenger
     * for sending messages to the service.
     */
    @Override
    public IBinder onBind(Intent intent) {
        Toast.makeText(getApplicationContext(), "binding", Toast.LENGTH_SHORT).show();
        Log.e(TAG, "onBind");
        return mMessenger.getBinder();
    }
}

参考 :
https://stackoverflow.com/questions/14746245/use-0-or-bind-auto-create-for-bindservices-flag
https://developer.android.com/guide/components/bound-services.html

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