為什么Messenger能進行進程間通信
Messenger翻譯為信使颓哮，他可以在不同的進程中傳遞Message對象
- 首先我們看下這個類的構(gòu)造方法钳垮，發(fā)現(xiàn)焙糟，他的底層實現(xiàn)其實就是AIDL蝗拿。
/**
* 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);
}
我們在跟一下Handler的getIMessenger方法晾捏，發(fā)現(xiàn)就是我們所熟悉的aidl的寫法。
final IMessenger getIMessenger() {
synchronized (mQueue) {
if (mMessenger != null) {
return mMessenger;
}
mMessenger = new MessengerImpl();
return mMessenger;
}
}
private final class MessengerImpl extends IMessenger.Stub {
public void send(Message msg) {
msg.sendingUid = Binder.getCallingUid();
Handler.this.sendMessage(msg);
}
}
使用Messenger如何實現(xiàn)進程間通信
- 首先我們先寫一個遠程服務端
public class MessengerService extends Service {
private static class MessengerHandler extends Handler {
@Override
public void handleMessage(@NonNull Message msg) {
switch (msg.what) {
case 1:
//接收到客戶端發(fā)來的消息
Log.d("MessengerService", msg.getData().getString("msg"));
//拿到客戶端的信使
Messenger reply = msg.replyTo;
Message replyMsg = Message.obtain(null,2);
Bundle bundle = new Bundle();
bundle.putString("reply","server receive this message");
replyMsg.setData(bundle);
try {
//給客戶端回消息
reply.send(replyMsg);
} catch (RemoteException e) {
e.printStackTrace();
}
break;
default:
super.handleMessage(msg);
break;
}
}
}
//創(chuàng)建一個服務端的信使哀托，同時傳入處理消息的handler對象
private final Messenger messenger = new Messenger(new MessengerHandler());
@Nullable
@Override
public IBinder onBind(Intent intent) {
//返回給客戶端binder對象
return messenger.getBinder();
}
}
- 在AndroidManifest.xml配置服務,process=":remote"使這個服務處于remote進程惦辛。
...
<service
android:name=".MessengerService"
android:process=":remote" />
...
- 編寫客戶端邏輯
public class MessengerActivity extends AppCompatActivity {
private static class ClientMessengerHandler extends Handler {
@Override
public void handleMessage(@NonNull Message msg) {
switch (msg.what) {
case 2:
//接收到服務端回的消息
Log.d("MessengerService", msg.getData().getString("reply"));
break;
default:
super.handleMessage(msg);
break;
}
}
}
/**
* 客戶端處理消息的信使
*/
private final Messenger clientMessengerHandler = new Messenger(new ClientMessengerHandler());
private Messenger serviceMessenger;
private ServiceConnection serviceConnection = new ServiceConnection() {
@Override
public void onServiceConnected(ComponentName name, IBinder service) {
//通過IBinder對象，創(chuàng)建出服務端的信使
serviceMessenger = new Messenger(service);
Message msg = Message.obtain(null, 1);
Bundle bundle = new Bundle();
bundle.putString("msg","hello this is client");
msg.setData(bundle);
//通過這種方式仓手，把客戶端的信使傳遞給服務端胖齐，用于服務端給客戶端回消息
msg.replyTo = clientMessengerHandler;
try {
//給服務端發(fā)送消息
serviceMessenger.send(msg);
} catch (RemoteException e) {
e.printStackTrace();
}
}
@Override
public void onServiceDisconnected(ComponentName name) {
}
};
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_messenger);
Intent it = new Intent(this,MessengerService.class);
bindService(it,serviceConnection, Context.BIND_AUTO_CREATE);
}
}
Messenger工作原理圖
Messenger工作原理圖
總結(jié)
- Messenger對AIDL進行了封裝，由于他一次處理一個請求嗽冒，因此在服務端我們不需要考慮線程同步問題
- Messenger進行數(shù)據(jù)傳遞必須將數(shù)據(jù)放到Message里面
- 由于Messenger一次處理一個請求呀伙，所有不適用于大量并發(fā)的請求
- Messenger作用主要是為了傳遞消息，如果我們需求需要調(diào)用服務端的具體方法添坊，Messenger無法做到剿另。（需要使用AIDL,自己定義接口來實現(xiàn)此類需求）
Thanks
鏈接: Android開發(fā)藝術探索.
