Running code in main thread from another thread

Question

In an android service I have created thread(s) for doing some background task.

I have a situation where a thread needs to post certain task on main thread's message queue, for example a Runnable.

Is there a way to get Handler of the main thread and post Message/Runnable to it from my other thread?

Answer 1

NOTE: This answer has gotten so much attention, that I need to update it. Since the original answer was posted, the comment from @dzeikei has gotten almost as much attention as the original answer. So here are 2 possible solutions:

1. If your background thread has a reference to a Context object:

Make sure that your background worker threads have access to a Context object (can be the Application context or the Service context). Then just do this in the background worker thread:

// Get a handler that can be used to post to the main thread Handler mainHandler = new Handler(context.getMainLooper());  Runnable myRunnable = new Runnable() {     @Override      public void run() {....} // This is your code }; mainHandler.post(myRunnable); 

2. If your background thread does not have (or need) a Context object

(suggested by @dzeikei):

// Get a handler that can be used to post to the main thread Handler mainHandler = new Handler(Looper.getMainLooper());  Runnable myRunnable = new Runnable() {     @Override      public void run() {....} // This is your code }; mainHandler.post(myRunnable);