Android Messenger 跨进程通信
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如果你需要在不同进程间通信,你可以在Service中使用Messenger来实现进程中通信。
如果使用这种方式,Service中需要定义一个Handler对象(负责对客户端发送过来的Message进行响应)。
Messenger可以共享给client一个IBinder对象,client通过这个IBinder对象向Service发送Message,而前面提到的Handler对象是这一切的基础。
注:使用这种方式进行通信是不支持多线程的。
那就让我们来看看使用这种方式进行通信吧!
注:Service在声明时必须对外开放,即android:exported="true",且本文是通过Intent启动的Service,所以在声明时该Service可以接收特定的Action。
1、在Service中创建一个Handler对象,来处理从client发过来的Message
2、根据创建的Handler对象创建一个Messenger对象
3、使用Messenger的getBinder方法得到一个IBinder对象,并在Service的onBind方法中将其反出去
4、client在onServiceConnected中根据IBinder参数创建一个Messenger对象(可参考Messenger的构造函数)
5、client可以使用上一步得到的Messenger对象来给Service发送Message了
经过上面的五部我们就能让client与Service进行通信。client使用Messenger对象给Service发送Message后,Service中的Handler将会对消息作出响应。
上面实现的仅仅是单向通信,即client给Service发送消息,如果我需要Service给client发送消息又该怎样做呢?
其实,这也是很容易实现的,下面就让我们接着上面的步骤来实现双向通信吧~
6、在client中创建一个Handler对象,用于处理Service发过来的消息
7、根据client中的Handler对象创建一个client自己的Messenger对象
8、我们在第5步的时候获得了Service的Messenger对象,并通过它来给Service发送消息。这时候,我们将client的Messenger对象赋给待发送的Message对象的replyTo字段
9、在Service的Handler处理Message时将client的Messenger解析出来,并使用client的Messenger对象给client发送消息
这样我们就实现了client和Service的双向通信。client和Service都有自己的Handler和Messenger对象,使得对方可以给自己发送消息,值得注意的是client的Messenger是通过Message的replyTo传递给Service的。
Messenger:信使
官方文档解释:它引用了一个Handler对象,以便others能够向它发送消息(使用mMessenger.send(Message msg)方法)。该类允许跨进程间基于Message的通信(即两个进程间可以通过Message进行通信),在服务端使用Handler创建一个Messenger,客户端持有这个Messenger就可以与服务端通信了。
以前我们使用Handler+Message的方式进行通信,都是在同一个进程中,从线程持有一个主线程的Handler对象,并向主线程发送消息。
而Android既然可以使用bindler机制进行跨进行通信,所以我们当然可以将Handler与bindler结合起来进行跨进程发送消息。
查看API就可以发现,Messenger就是这种方式的实现。
一般使用方法如下:
1。远程通过
mMessenger = new Messenger(mHandler)
创建一个信使对象
2。客户端使用bindlerService请求连接远程
3。远程onBind方法返回一个bindler
return mMessenger.getBinder();
4.客户端使用远程返回的bindler得到一个信使(即得到远程信使)
public void onServiceConnected(ComponentName name, IBinder service) {
rMessenger = new Messenger(service);
......
}
这里虽然是new了一个Messenger,但我们查看它的实现
public Messenger(IBinder target) { mTarget = IMessenger.Stub.asInterface(target); }
发现它的mTarget是通过Aidl得到的,实际上就是远程创建的那个。
5。客户端可以使用这个远程信使对象向远程发送消息:rMessenger.send(msg);
这样远程服务端的Handler对象就能收到消息了,然后可以在其handlerMessage(Message msg)方法中进行处理。(该Handler对象就是第一步服务端创建Messenger时使用的参数mHandler).
经过这5个步骤貌似只有客户端向服务端发送消息,这样的消息传递是单向的,那么如何实现双向传递呢?
首先需要在第5步稍加修改,在send(msg)前通过msm.replyTo = mMessenger将自己的信使设置到消息中,这样服务端接收到消息时同时也得到了客户端的信使对象了,然后服务端可以通过/得到客户端的信使对象,并向它发送消息 cMessenger = msg.replyTo; cMessenger.send(message);
即完成了从服务端向客户端发送消息的功能,这样客服端可以在自己的Handler对象的handlerMessage方法中接收服务端发送来的message进行处理。
双向通信宣告完成。
以下代码来自ApiDemo
Service code:
[java]
-
public class MessengerService extends Service {
-
/** For showing and hiding our notification. */
-
NotificationManager mNM;
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/** Keeps track of all current registered clients. */
-
ArrayList<Messenger> mClients = new ArrayList<Messenger>();
-
/** Holds last value set by a client. */
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int mValue = 0;
-
-
/**
-
* Command to the service to register a client, receiving callbacks
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* from the service. The Message‘s replyTo field must be a Messenger of
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* the client where callbacks should be sent.
-
*/
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static final int MSG_REGISTER_CLIENT = 1;
-
-
/**
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* Command to the service to unregister a client, ot stop receiving callbacks
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* from the service. The Message‘s replyTo field must be a Messenger of
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* the client as previously given with MSG_REGISTER_CLIENT.
-
*/
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static final int MSG_UNREGISTER_CLIENT = 2;
-
-
/**
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* Command to service to set a new value. This can be sent to the
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* service to supply a new value, and will be sent by the service to
-
* any registered clients with the new value.
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*/
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static final int MSG_SET_VALUE = 3;
-
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/**
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* Handler of incoming messages from clients.
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*/
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class IncomingHandler extends Handler {
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@Override
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public void handleMessage(Message msg) {
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switch (msg.what) {
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case MSG_REGISTER_CLIENT:
-
mClients.add(msg.replyTo);
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break;
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case MSG_UNREGISTER_CLIENT:
-
mClients.remove(msg.replyTo);
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break;
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case MSG_SET_VALUE:
-
mValue = msg.arg1;
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for (int i = mClients.size() - 1; i >= 0; i --) {
-
try {
-
mClients.get(i).send(Message.obtain(null,
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MSG_SET_VALUE, mValue, 0));
-
} catch (RemoteException e) {
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// The client is dead. Remove it from the list;
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// we are going through the list from back to front
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// so this is safe to do inside the loop.
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mClients.remove(i);
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}
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}
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break;
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default:
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super.handleMessage(msg);
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}
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}
-
}
-
-
/**
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* Target we publish for clients to send messages to IncomingHandler.
-
*/
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final Messenger mMessenger = new Messenger(new IncomingHandler());
-
-
@Override
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public void onCreate() {
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mNM = (NotificationManager)getSystemService(NOTIFICATION_SERVICE);
-
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// Display a notification about us starting.
-
showNotification();
-
}
-
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@Override
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public void onDestroy() {
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// Cancel the persistent notification.
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mNM.cancel(R.string.remote_service_started);
-
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// Tell the user we stopped.
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Toast.makeText(this, R.string.remote_service_stopped, Toast.LENGTH_SHORT).show();
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}
-
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/**
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* When binding to the service, we return an interface to our messenger
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* for sending messages to the service.
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*/
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@Override
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public IBinder onBind(Intent intent) {
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return mMessenger.getBinder();
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}
-
-
/**
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* Show a notification while this service is running.
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*/
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private void showNotification() {
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// In this sample, we‘ll use the same text for the ticker and the expanded notification
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CharSequence text = getText(R.string.remote_service_started);
-
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// Set the icon, scrolling text and timestamp
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Notification notification = new Notification(R.drawable.stat_sample, text,
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System.currentTimeMillis());
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// The PendingIntent to launch our activity if the user selects this notification
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PendingIntent contentIntent = PendingIntent.getActivity(this, 0,
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new Intent(this, Controller.class), 0);
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// Set the info for the views that show in the notification panel.
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notification.setLatestEventInfo(this, getText(R.string.remote_service_label),
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text, contentIntent);
-
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// Send the notification.
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// We use a string id because it is a unique number. We use it later to cancel.
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mNM.notify(R.string.remote_service_started, notification);
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}
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}
Client code:
[java]
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public class MessengerServiceActivities {
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/**
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* Example of binding and unbinding to the remote service.
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* This demonstrates the implementation of a service which the client will
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* bind to, interacting with it through an aidl interface.</p>
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*
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* <p>Note that this is implemented as an inner class only keep the sample
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* all together; typically this code would appear in some separate class.
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*/
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public static class Binding extends Activity {
-
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/** Messenger for communicating with service. */
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Messenger mService = null;
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/** Flag indicating whether we have called bind on the service. */
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boolean mIsBound;
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/** Some text view we are using to show state information. */
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TextView mCallbackText;
-
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/**
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* Handler of incoming messages from service.
-
*/
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class IncomingHandler extends Handler {
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@Override
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public void handleMessage(Message msg) {
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switch (msg.what) {
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case MessengerService.MSG_SET_VALUE:
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mCallbackText.setText("Received from service: " + msg.arg1);
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break;
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default:
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super.handleMessage(msg);
-
}
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}
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}
-
-
/**
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* Target we publish for clients to send messages to IncomingHandler.
-
*/
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final Messenger mMessenger = new Messenger(new IncomingHandler());
-
-
/**
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* Class for interacting with the main interface of the service.
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*/
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private ServiceConnection mConnection = new ServiceConnection() {
-
public void onServiceConnected(ComponentName className,
-
IBinder service) {
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// This is called when the connection with the service has been
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// established, giving us the service object we can use to
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// interact with the service. We are communicating with our
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// service through an IDL interface, so get a client-side
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// representation of that from the raw service object.
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mService = new Messenger(service);
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mCallbackText.setText("Attached.");
-
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// We want to monitor the service for as long as we are
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// connected to it.
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try {
-
Message msg = Message.obtain(null,
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MessengerService.MSG_REGISTER_CLIENT);
-
msg.replyTo = mMessenger;
-
mService.send(msg);
-
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// Give it some value as an example.
-
-
msg = Message.obtain(null,
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MessengerService.MSG_SET_VALUE, this.hashCode(), 0);
-
-
mService.send(msg);
-
} catch (RemoteException e) {
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// In this case the service has crashed before we could even
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// do anything with it; we can count on soon being
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// disconnected (and then reconnected if it can be restarted)
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// so there is no need to do anything here.
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}
-
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// As part of the sample, tell the user what happened.
-
Toast.makeText(Binding.this, R.string.remote_service_connected,
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Toast.LENGTH_SHORT).show();
-
}
-
-
public void onServiceDisconnected(ComponentName className) {
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// This is called when the connection with the service has been
-
// unexpectedly disconnected -- that is, its process crashed.
-
mService = null;
-
mCallbackText.setText("Disconnected.");
-
-
// As part of the sample, tell the user what happened.
-
Toast.makeText(Binding.this, R.string.remote_service_disconnected,
-
Toast.LENGTH_SHORT).show();
-
}
-
};
-
-
void doBindService() {
-
// Establish a connection with the service. We use an explicit
-
// class name because there is no reason to be able to let other
-
// applications replace our component.
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bindService(new Intent(Binding.this,
-
MessengerService.class), mConnection, Context.BIND_AUTO_CREATE);
-
mIsBound = true;
-
mCallbackText.setText("Binding.");
-
}
-
-
void doUnbindService() {
-
if (mIsBound) {
-
// If we have received the service, and hence registered with
-
// it, then now is the time to unregister.
-
if (mService != null) {
-
try {
-
Message msg = Message.obtain(null,
-
MessengerService.MSG_UNREGISTER_CLIENT);
-
msg.replyTo = mMessenger;
-
mService.send(msg);
-
} catch (RemoteException e) {
-
// There is nothing special we need to do if the service
-
// has crashed.
-
}
-
}
-
-
// Detach our existing connection.
-
unbindService(mConnection);
-
mIsBound = false;
-
mCallbackText.setText("Unbinding.");
-
}
-
}
-
-
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/**
-
* Standard initialization of this activity. Set up the UI, then wait
-
* for the user to poke it before doing anything.
-
*/
-
@Override
-
protected void onCreate(Bundle savedInstanceState) {
-
super.onCreate(savedInstanceState);
-
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setContentView(R.layout.messenger_service_binding);
-
-
// Watch for button clicks.
-
Button button = (Button)findViewById(R.id.bind);
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button.setOnClickListener(mBindListener);
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button = (Button)findViewById(R.id.unbind);
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button.setOnClickListener(mUnbindListener);
-
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mCallbackText = (TextView)findViewById(R.id.callback);
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mCallbackText.setText("Not attached.");
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}
-
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private OnClickListener mBindListener = new OnClickListener() {
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public void onClick(View v) {
-
doBindService();
-
}
-
};
-
-
private OnClickListener mUnbindListener = new OnClickListener() {
-
public void onClick(View v) {
-
doUnbindService();
-
}
-
};
-
}
-
}
register:
[html]
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< service Android:name=".app.MessengerService"
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android:process=":remote" />
原文:http://my.oschina.net/u/165172/blog/308806
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