利用Messenger实现同一进程Activity和Service之间的通信

今天突然发现使用Messenger不止可以实现进程间通信,它实际上是一种标准的通信模式,同一进程一样可以通信

1.Activity向Service发送信息

1) 首先在Service中定义一个Service专用的Handler,并重写onBind()方法将Handler包装之后返回

public class MessengerService extends Service {

    Handler serviceHandler = new Handler(){
        @Override
        public void handleMessage(Message msg) {
            super.handleMessage(msg);
        }
    };

    @Nullable
    @Override
    public IBinder onBind(Intent intent) {
        Messenger messenger = new Messenger(serviceHandler);
        return messenger.getBinder();       //Activity在bindService时就会获得这个IBinder对象
    }
}

2)通过bindService()在Activity中获取可以向Service发送消息的Messenger对象

Messenger serviceMessenger; //在Activity中定义一个成员变量serviceMessenger,这个对象专门用来向Service发送信息

ServiceConnection conn = new ServiceConnection() {
    @Override
    public void onServiceConnected(ComponentName name, IBinder service) {
        serviceMessenger = new Messenger(service);      //这样在使用bindService()方法之后,serviceMessenger就可以向Service发送信息了
    }

    @Override
    public void onServiceDisconnected(ComponentName name) {

    }
};

发送信息

private void sendMessage() {        //实际上这个message是发送到了Service的Handler中去
    Message message = Message.obtain();   
    try {
        serviceMessenger.send(message);   //因为Messenger可用于远程通信,所以要try-catch
    } catch (RemoteException e) {
        e.printStackTrace();
    }
}

2.Service向Activity发送信息

1) 先在Activity中定义一个Handler用来接受Service发送的信息

Handler activityHandler = new Handler(Looper.getMainLooper()){
    @Override
    public void handleMessage(Message msg) {
        super.handleMessage(msg);
    }
};

2) 既然已经有了向Service发送信息的能力了,那就直接把Handler包装在Messenger中发送给Service

Messenger activityMessenger = new Messenger(activityHandler);   //包装Activity的handler
Message message = Message.obtain();
message.what = MessengerService.GET_ACTIVITY_MESSENGER;
message.replyTo = activityMessenger;
try {
    serviceMessenger.send(message);     //实际上是将message发送给Service的Handler处理
} catch (RemoteException e) {
    e.printStackTrace();
}

3) Service获取Messenger

public static final int GET_ACTIVITY_MESSENGER = -2;

Messenger activityMessenger = null;

Handler serviceHandler = new Handler() {
    @Override
    public void handleMessage(Message msg) {
        switch (msg.what){
            case GET_ACTIVITY_MESSENGER:    //标识
                activityMessenger = msg.replyTo;    //获取了Activity的Messenger
                break;
        }
    }
};

4) Service向Activity发送信息

    private void sendSomethingToActivity(){
        Message message = Message.obtain();
        //这里添加message需要携带的信息
        try {
            activityMessenger.send(message);    //实际上是将message发送给了Activity的Handler来处理
        } catch (RemoteException e) {
            e.printStackTrace();
        }
    }

3. 互相发送信息

到这也应该明白了,要向对方发送信息,直接调用Messenger的send()方法就可以把携带信息的message发送给对方了

//Activity发送给Service
private void sendSomethingToService(){
    Message message = Message.obtain();
    //添加发送的信息到message中
    try {
        serviceMessenger.send(message);
    } catch (RemoteException e) {
        e.printStackTrace();
    }
}




//Service发送给Activity
private void sendSomethingToActivity(){
    Message message = Message.obtain();
    //添加发送的信息到message中
    try {
        activityMessenger.send(message);
    } catch (RemoteException e) {
        e.printStackTrace();
    }
}

看起来写得麻烦,实际上降低了两个类的依赖,对以后的扩展很有帮助

因为这个是个固定的写法,甚至可以直接写进BaseActivity中或者BaseService中