InterAppCommunication

Introduction

This tutorial covers the mechanism for performing Inter-App Communication. It comes with two apps. A client app that makes the request and a service app that processes the request and sends a response back.

Step 1: Create the Service

You must create a service that will be bound to before invocation. The service must return an IBinder object during the onBind invocation

public class RemoteService extends Service

{

        private Messenger messenger; //receives remote invocations

        

        @Override

        public IBinder onBind(Intent intent) 

        {

                if(this.messenger == null)

                {

                        synchronized(RemoteService.class)

                        {

                                if(this.messenger == null)

                                {

                                        this.messenger = new Messenger(new IncomingHandler());

                                }

                        }

                }

                //Return the proper IBinder instance

                return this.messenger.getBinder();

        }

The service uses a Messenger and sends it binder back. A Messenger is the component that makes inter process communication possible.

Step 2: Implement the Handler

Handler is the component that is registered with the Messenger. This component is the one that receives the remote invocation.

private class IncomingHandler extends Handler

        {

                @Override

        public void handleMessage(Message msg) 

                {

                        System.out.println("*****************************************");

                        System.out.println("Remote Service successfully invoked!!!!!!");

                        System.out.println("*****************************************");

                        

                        int what = msg.what;

                        

                        Toast.makeText(RemoteService.this.getApplicationContext(), "Remote Service invoked-("+what+")", Toast.LENGTH_LONG).show();

                        

                        //Setup the reply message

                        Message message = Message.obtain(null, 2, 0, 0);

                        try

                        {

                                //make the RPC invocation

                                Messenger replyTo = msg.replyTo;

                                replyTo.send(message);

                        }

                        catch(RemoteException rme)

                        {

                                //Show an Error Message

                                Toast.makeText(RemoteService.this, "Invocation Failed!!", Toast.LENGTH_LONG).show();

                        }

        }

        }

This Handler processes the incoming request and sends a reply based on the replyTo Messenger that comes in with the incoming request.

Full Src for the Service implementation

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