「Android」基于轻量级Messenger的进程通信 android

「Android」基于轻量级Messenger的进程通信 Android中目前存在多种IPC方式，分别为：

Bundle
文件共享
Messenger
AIDL
ContentProvider
Socket

Messenger 【「Android」基于轻量级Messenger的进程通信】Messenger是一种轻量级的IPC方案，它的底层实现是基于AIDL：

/** * Create a new Messenger pointing to the given Handler.Any Message * objects sent through this Messenger will appear in the Handler as if * {@link Handler#sendMessage(Message) Handler.sendMessage(Message)} had * been called directly. * * @param target The Handler that will receive sent messages. */ public Messenger(Handler target) { mTarget = target.getIMessenger(); }/** * Create a Messenger from a raw IBinder, which had previously been * retrieved with {@link #getBinder}. * * @param target The IBinder this Messenger should communicate with. */ public Messenger(IBinder target) { mTarget = IMessenger.Stub.asInterface(target); }

Messenger对AIDL做了封装，使得我们可以更简便的进行进程通信。同时，它一次处理一个请求，不存在并发执行的情形，因此在服务端不需要考虑线程同步问题。
Messenger原理图
实现一个Messenger主要分为Server端和Client端：

Server端
需要在Server端创建一个Service来处理Client端的连接请求，同时创建一个Handler对象并通过它来创建一个Messenger对象，然后在Service的onBind中()方法返回这个Messenger对象底层的Binder。
Client端
首先需要绑定Server端的Service，绑定成功后即可获取到Server端返回的IBinder对象并通过它创建一个Messenger对象，通过这个Messenger对象就可以向Server端发送消息，发消息的类型为Message对象。
如果需要Server端回应Client端，如同Server端一样，Client端也需要创建一个Handler对象并通过它来创建一个Messenger对象，并把这个Messenger对象通过Message的replyTo参数传递给Server端。
Server端可通过这个replyTo参数获取到Client端的Messenger对象，并通过这个Messenger对象就可以向Client端发送消息

Server端示例代码

public class MessengerService extends Service {private static class ServerMessengerHandler extends Handler { @Override public void handleMessage(Message msg) { switch (msg.what) { case MSG_FROM_CLIENT: // 通过Message，获取Client端的Messenger对象 mClientMessenger = msg.replyTo; Message replyMessage = Message.obtain(null, MSG_FROM_SERVER); Bundle bundle = new Bundle(); // 将data，添加进Message bundle.putString(DATA, DATA); replyMessage.setData(bundle); try { // 向Client端发送Message mClientMessenger.send(replyMessage); } catch (RemoteException e) { e.printStackTrace(); } break; } } }private final Messenger mServerMessenger = new Messenger(new ServerMessengerHandler()); private Messenger mClientMessenger; @Override public IBinder onBind(Intent intent) { return mServerMessenger.getBinder(); } }

Client端示例代码

public class MessengerClient extends Context{private static class ClientMessengerHandler extends Handler { @Override public void handleMessage(Message msg) { switch (msg.what) { case MSG_FROM_SERVER: // 获取data String data = https://www.it610.com/article/msg.getData().getString(DATA); break; } } }private boolean mBound; private final Messenger mClientMessenger = new Messenger(new ClientMessengerHandler()); private Messenger mServerMessenger; private ServiceConnection mConnection = new ServiceConnection() { @Override public void onServiceConnected(ComponentName name, IBinder service) { // 通过IBinder对象，获取Server端的Messenger对象 mServerMessenger = new Messenger(service); mBound = true; Message requestMessage = Message.obtain(null, MSG_FROM_CLIENT); Bundle bundle = new Bundle(); bundle.putString(REQUEST, REQUEST); requestMessage.setData(bundle); // 将Client端的Messenger对象，添加进Message mClientMessenger = new Messenger(mHandler); requestMessage.replyTo = mClientMessenger; try { // 向Server端发送Message mServerMessenger.send(msg); } catch (RemoteException e) { e.printStackTrace(); } }@Override public void onServiceDisconnected(ComponentName name) { mServerMessenger = null; mBound = false; } }// 请求data // Client端触发基于Messenger的IPC流程 private void doBindService() { Intent intent = new Intent(this, MessengerServer.class); bindService(intent, mConnection, Context.BIND_AUTO_CREATE); } }

IPC方式的优缺点和适用场景

方式	能力	特点	适用场景
AIDL	支持一对多并发通信、支持实时通信、支持跨进程函数调用	需要独立定义.aidl规范、需要添加.aidl文件、使用较复杂	一对多即时通信，有RPC需求
Messenger	支持一对多串行通信、支持实时通信、支持Bundle传递	无需独立定义.aidl规范、无需添加.aidl文件、使用较简洁	低并发的一对多即时通信，无返回结果的RPC需求