How to get back a reply through a message in Android activity

Question

How can I get back a Message reply to the Activity in Android? Say an Activity ask one of a java object (Running Thread) to do something and give back the reply. How java object can know to reply back to the activity who sent the message? I have many activities and many objects communicate with each other.
How can I implement this with Android Messages? I don't want to use broadcasting here.

Answer 1

We can use Messenger for this. Can set the messenger as the reply path. And inside message it hold the handler it should give back the reply.

final Messenger messenger = new Messenger(handler); 
. 
.
msg.replyTo = messenger;  // set the handler of the reply activity.
msg.setData(mBundle);     // if any additional data available put to a bundle
destinationClass.mHandler.sendMessage(msg);



// in destination class

Messenger msger = msg.replyTo;  // get the message sender's details.

Message msg2 = Message.obtain();
msger.send(msg2);                // send the reply message again to the sender

Answer 2

You can use a Handler if you are trying to communicate with a Thread. From the docs

Handler is part of the Android system's framework for managing threads. A Handler object receives messages and runs code to handle the messages.

A nice article on this topic: AndroidBackgroundProcessing

Answer 3

A possible approach is Callbacks. Call backs in Java (code explanation) or an observer pattern http://www.vogella.com/articles/DesignPatternObserver/article.html