Use of Messenger in Android

We use handler in a process, how do we use handler across processes?

In fact, this problem is not difficult to solve, self-made to the binder for some encapsulation can be easily implemented. But when you look at the system source code, you will find that, in fact, these Android have been done for us.

using the Android system Android.os.Messenger It is convenient to use handler across processes. The following is an example program.

The first is the service side.

public class messengertestservice extends service {      protected static final string tag =  "Messengertestservice";          private handler mhandler = new handler ()  {          @Override          Public void handlemessage (message msg)  {             switch  (msg.what)  {             case 1:                 LOG.D (tag,  "received message");                  //get Messenger in client message for callback                  final messenger callback = msg.replyto;                 try {                     //  Callback                       callback.send (Message.obtain (null, 0));                 } catch  (remoteexception e)  {                     // todo  Auto-generated catch block                     e.printstacktrace ();                 }                 break;            }         }    };           @Override     public ibinder onbind (intent intent)  {         return new messenger (MHandler). GetBinder ();     } }

Then the client

public class mainactivity extends activity {     protected  static final String TAG =  "Mainactivity";     messenger  messenger;    Messenger reply;           @Override     protected void oncreate (bundle savedinstancestate)   {        super.oncreate (savedinstancestate);         setcontentview (R.layout.activity_main);         reply = new messenger (handler);         intent  intent = new intent ();         intent.setclassname ("Test.messenger",  "Test.messenger.MessengerTestService");                  //  Binding Service         bindservice (intent,  new serviceconnection ()  {                           @Override              public void onservicedisconnected ( Componentname name)  {                              }                            @Override              public void onserviceconnected (Componentname name, ibinder service)  {        &Nbsp;        toast.maketext (mainactivity.this,  "bind success ",  0). Show ();                 messenger = new messenger (Service);             }        }, context.bind_auto_create);              }     public  void sendmessage (VIEW V)  {        Message  Msg = message.obtain (null, 1);        //  Sets the messenger        msg.replyto = reply;   of the call back       try {             messenger.send (msg);         } catch  (remoteexception e)  {             e.printstacktrace ();         }    }         private  handler handler = new handler ()  {           @Override         public void handlemessage ( message msg)  {            log.d (TAG,   "Callback succeeded");        }              };}

The client binds the server side, obtaining the Binder object for remote Messenger. Call Messenger's send function, and you can send the message to the handler on the server.

At the same time, if you need a server callback client (handler to the client), you can set the ReplyTo in the Send message, and the server can send messages to the client.

Below we look at the source of Messenger, or is very simple.

constructor function

Public Messenger (Handler target) {mtarget = Target.getimessenger (); }

Handler.getimessenger () returns a IMessenger binder object whose send method will invoke the SendMessage method of Handler.

public void Send (Message message) throws RemoteException {mtarget.send (message); }

Use of Messenger in Android