Messenger通信原理
Messenger其實是谷歌對aidl進行的封裝,用來處理簡單的跨程序通信。那麼如何用Messenger傳遞資訊呢?
單向通信
現在假設我們有服務端和用戶端,并且服務端與用戶端不在同一程序中。
首先服務端需要建立一個Handler用來接收用戶端發送來的消息,然後利用這個handler,來構造一個Messenger,并且在onBind方法中将messenger的IBinder傳回給用戶端。那麼當用戶端通過bindService方法綁定這個服務之後,就可以通過這個IBinder對象來構造一個Messenger對象,然後就可以發送Message類型的消息,進而實作一個單向跨程序通信。
這麼說可能有些抽象,下面我貼上實作代碼,看完就應該很容易了解了。
//服務端代碼
RemoteService.class
public class RemoteService extends Service {
private static final String TAG = "RemoteService";
private Handler receiveHandler = new Handler(){
@Override
public void handleMessage(Message msg) {
switch (msg.what){
case 0:
Log.d(TAG,"收到了用戶端發來的消息:" + msg.getData().getString("client_message"));
break;
default:
super.handleMessage(msg);
}
}
};
//這裡利用一個Handler對象構造一個Messenger對象
private Messenger messenger = new Messenger(receiveHandler);
public RemoteService() {
}
@Override
public IBinder onBind(Intent intent) {
return messenger.getBinder();
}
}
這裡要注意,由于示範的是跨程序通信,但是為了友善我并沒有寫兩個應用,而是在service的配置中開了一個程序
AndroidManifest.xml
<service
android:process=":remote"
android:name=".service.RemoteService"
android:enabled="true"
android:exported="true"></service>
//用戶端代碼
MainActivity.class
public class MainActivity extends AppCompatActivity {
private Messenger messenger;
private ServiceConnection mConnection = new ServiceConnection(){
@Override
public void onServiceConnected(ComponentName name, IBinder service) {
//這裡利用一個IBinder對象構造一個Messenger對象
messenger = new Messenger(service);
Message msg = Message.obtain(null, 0);
Bundle bundle = new Bundle();
bundle.putString("client_message","I'm from Client!");
msg.setData(bundle);
try {
messenger.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_main);
final Intent intent = new Intent(this, RemoteService.class);
//綁定服務按鈕
Button btnBind = (Button) findViewById(R.id.btn_bind);
btnBind.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
bindService(intent, mConnection, BIND_AUTO_CREATE);
}
});
}
}
當我們點選綁定服務按鈕時,控制台就會輸出一條資訊:
D/RemoteService: 收到了用戶端發來的消息:I'm from Client!。
下面說一下雙向通信:
要實作雙向通信,那麼用戶端也需要建立一個Handler對象來接收服務端發來的消息。
然後同樣,利用這個Handler對象來構造一個Messenger對象,并且在給服務端發消息時,
給Message對象的replyTo屬性指派,也就是msg.replyTo = clientMessenger;
那麼服務端如何給用戶端發消息呢?
其實很容易,就是利用剛才的msg.replyTo來擷取用戶端Messenger,然後發送消息。
雙向通信代碼(跨程序)
//服務端代碼
RemoteService.class
public class RemoteService extends Service {
private static final String TAG = "RemoteService";
private Handler receiveHandler = new Handler(){
@Override
public void handleMessage(Message msg) {
switch (msg.what){
case 0:
Log.d(TAG,"收到了用戶端發來的消息:" + msg.getData().getString("client_message"));
//在這裡得到用戶端的Messenger
Messenger clientMessenger = msg.replyTo;
Message msg1 = Message.obtain(null, 0);
Bundle bundle = new Bundle();
bundle.putString("server_message","I'm from Server!");
msg1.setData(bundle);
try {
clientMessenger.send(msg1);
} catch (RemoteException e) {
e.printStackTrace();
}
break;
default:
super.handleMessage(msg);
}
}
};
private Messenger messenger = new Messenger(receiveHandler);
public RemoteService() {
}
@Override
public IBinder onBind(Intent intent) {
return messenger.getBinder();
}
}
//用戶端代碼
MainActivity.class
public class MainActivity extends AppCompatActivity {
private Messenger messenger;
private ServiceConnection mConnection = new ServiceConnection(){
@Override
public void onServiceConnected(ComponentName name, IBinder service) {
//這裡利用一個IBinder對象構造一個Messenger對象
messenger = new Messenger(service);
Message msg = Message.obtain(null, 0);
Bundle bundle = new Bundle();
bundle.putString("client_message","I'm from Client!");
msg.setData(bundle);
//這裡就是把用戶端的Messenger傳遞過去
msg.replyTo = clientMessenger;
try {
messenger.send(msg);
} catch (RemoteException e) {
e.printStackTrace();
}
}
@Override
public void onServiceDisconnected(ComponentName name) {
}
};
private Handler clientHandler = new Handler(){
@Override
public void handleMessage(Message msg) {
switch (msg.what){
case 0:
Log.d("MainActivity","收到了服務端傳回的消息:"+msg.getData().getString("server_message"));
break;
default:
super.handleMessage(msg);
}
}
};
private Messenger clientMessenger = new Messenger(clientHandler);
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
final Intent intent = new Intent(this, RemoteService.class);
//綁定服務按鈕
Button btnBind = (Button) findViewById(R.id.btn_bind);
btnBind.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
bindService(intent, mConnection, BIND_AUTO_CREATE);
}
});
}
}
當我們點選綁定服務按鈕時,控制台就會輸出這兩條資訊:
D/RemoteService: 收到了用戶端發來的消息:I'm from Client!。
D/MainActivity: 收到了服務端傳回的消息:I'm from Server!