samples/ApiDemos/src/com/example/android/apis/app/MessengerServiceActivities.java

package com.example.android.apis.app;

import com.example.android.apis.R;
import com.example.android.apis.app.LocalServiceActivities.Binding;

import android.app.Activity;
import android.content.ComponentName;
import android.content.Context;
import android.content.Intent;
import android.content.ServiceConnection;
import android.os.Bundle;
import android.os.Handler;
import android.os.IBinder;
import android.os.Message;
import android.os.Messenger;
import android.os.RemoteException;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.TextView;
import android.widget.Toast;

public class MessengerServiceActivities {

// BEGIN_INCLUDE(bind)
    /**
     * Example of binding and unbinding to the remote service.
     * This demonstrates the implementation of a service which the client will
     * bind to, interacting with it through an aidl interface.
     * 
     * Note that this is implemented as an inner class only keep the sample
     * all together; typically this code would appear in some separate class.
     */
    public static class Binding extends Activity {
        /** Messenger for communicating with service. */
        Messenger mService = null;
        /** Flag indicating whether we have called bind on the service. */
        boolean mIsBound;
        /** Some text view we are using to show state information. */
        TextView mCallbackText;
        
        /**
         * Handler of incoming messages from service.
         */
        class IncomingHandler extends Handler {
            @Override
            public void handleMessage(Message msg) {
                switch (msg.what) {
                    case MessengerService.MSG_SET_VALUE:
                        mCallbackText.setText("Received from service: " + msg.arg1);
                        break;
                    default:
                        super.handleMessage(msg);
                }
            }
        }
        
        /**
         * Target we publish for clients to send messages to IncomingHandler.
         */
        final Messenger mMessenger = new Messenger(new IncomingHandler());
        
        /**
         * Class for interacting with the main interface of the service.
         */
        private ServiceConnection mConnection = new ServiceConnection() {
            public void onServiceConnected(ComponentName className,
                    IBinder service) {
                // This is called when the connection with the service has been
                // established, giving us the service object we can use to
                // interact with the service.  We are communicating with our
                // service through an IDL interface, so get a client-side
                // representation of that from the raw service object.
                mService = new Messenger(service);
                mCallbackText.setText("Attached.");

                // We want to monitor the service for as long as we are
                // connected to it.
                try {
                    Message msg = Message.obtain(null,
                            MessengerService.MSG_REGISTER_CLIENT);
                    msg.replyTo = mMessenger;
                    mService.send(msg);
                    
                    // Give it some value as an example.
                    msg = Message.obtain(null,
                            MessengerService.MSG_SET_VALUE, this.hashCode(), 0);
                    mService.send(msg);
                } catch (RemoteException e) {
                    // In this case the service has crashed before we could even
                    // do anything with it; we can count on soon being
                    // disconnected (and then reconnected if it can be restarted)
                    // so there is no need to do anything here.
                }
                
                // As part of the sample, tell the user what happened.
                Toast.makeText(Binding.this, R.string.remote_service_connected,
                        Toast.LENGTH_SHORT).show();
            }

            public void onServiceDisconnected(ComponentName className) {
                // 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.
            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.");
            }
        }
 // END_INCLUDE(bind)
        
        /**
         * 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);

            setContentView(R.layout.messenger_service_binding);

            // Watch for button clicks.
            Button button = (Button)findViewById(R.id.bind);
            button.setOnClickListener(mBindListener);
            button = (Button)findViewById(R.id.unbind);
            button.setOnClickListener(mUnbindListener);
            
            mCallbackText = (TextView)findViewById(R.id.callback);
            mCallbackText.setText("Not attached.");
        }

        private OnClickListener mBindListener = new OnClickListener() {
            public void onClick(View v) {
                doBindService();
            }
        };

        private OnClickListener mUnbindListener = new OnClickListener() {
            public void onClick(View v) {
                doUnbindService();
            }
        };
    }
}