Question

1. I have Activity with Handler (UI thread)
2. I start new Thread and make handler.post(new MyRunnable()) – (new work thread)

Android documentation said about post method: “Causes the Runnable r to be added to the message queue. The runnable will be run on the thread to which this handler is attached.”

Handler attached to UI thread.
How android can run runnable in the same UI thread without new thread creation?

Is new thread will be created using Runnable from handler.post()?
Or it’s only run() method will be called from Runnable subclass?

Answer 1

Handler attached to UI thread.

Correct.

How android can run runnable in the same UI thread without new thread creation?

Any thread, including the main application (“UI”) thread, can call post() on Handler (or on any View, for that matter).