The Android Developer’s Cookbook: Building Applications with the Android SDK, Second Edition (2013)

public class MessengerActivity extends Activity {
private static final String LOG_TAG = null;

EditText editText;

/** messenger for communicating with service */
Messenger mServiceMessenger = null;
/** flag indicating whether we have called bind on the service */
boolean mIsBound;


protected Handler mHandler = new Handler() {
@Override
public void handleMessage(Message msg) {
if(msg.what==MessageControlledService.MSG_RESULT){
Toast.makeText(
getApplicationContext(),
(String)msg.obj,
Toast.LENGTH_SHORT
).show();
}
}

};

Messenger mLocalMessageReceiver=new Messenger(mHandler);

/**
* class for interacting with the main interface of the service
*/
private final ServiceConnection mServiceConnection = new ServiceConnection() {
@Override
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.
mServiceMessenger = new Messenger(service);

// We want to monitor the service for as long as we are
// connected to it
try {
Message msg = Message.obtain(null,
MessageControlledService.MSG_REGISTER_CLIENT);
msg.replyTo = mLocalMessageReceiver;
mServiceMessenger.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.
}

Log.v(LOG_TAG, "service connected");
}

@Override
public void onServiceDisconnected(ComponentName className) {
// This is called when the connection with the service has been
// unexpectedly disconnected--that is, its process crashed
mServiceMessenger = null;
Log.v(LOG_TAG, "service disconnected");

}
};



@Override
protected void onResume() {
super.onResume();
bindMessengerService();
}

@Override
protected void onPause() {
super.onPause();
unbindAccountService();
}

void bindMessengerService() {
Log.v(LOG_TAG,"binding accountservice");
// Establish a connection with the service. We use an explicit
// class name because there is no reason to let other
// applications replace our component.
bindService(new Intent(getApplicationContext(),
MessageControlledService.class),
mServiceConnection, Context.BIND_AUTO_CREATE);
mIsBound = true;

}

protected void unbindAccountService() {
if (mIsBound) {
Log.v(LOG_TAG,"unbinding accountservice");
// If we have received the service, and hence registered with
// it, now is the time to unregister
if (mServiceMessenger != null) {

try
{
Message msg=Message.obtain(
null,
MessageControlledService.MSG_UNREGISTER_CLIENT
);

msg.replyTo = mServiceMessenger;

mServiceMessenger.send(msg);

} catch (RemoteException e) {

// There is nothing special we need to do if the service

// has crashed
}
}

// Detach our existing connection
unbindService(mServiceConnection);
mIsBound = false;

}
}

protected boolean sendMessageToService(final int what,
final int arg1,final int arg2,
final Object object) {
try {
Message msg = Message.obtain(null, what, arg1, arg2, object);
mServiceMessenger.send(msg);
} catch (RemoteException e) {
Log.e(LOG_TAG,"unable to send message to account service",e);
//Retry binding
bindMessengerService();
return false;
}
return true;

}
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
startService(new Intent(getApplicationContext(),
MessageControlledService.class));
setContentView(R.layout.main);

editText=(EditText) findViewById(R.id.editText1);

Button sendButton = (Button) findViewById(R.id.Button01);
sendButton.setOnClickListener(new View.OnClickListener() {
public void onClick(View view){
String text=editText.getText().toString();
sendMessageToService(MessageControlledService.MSG_FIRST_USER,
-1,-1,text);
}
});


}

}