Android - can mainThread handlers cause memory leaks?

Question

I am curious why the below is a memory leak because the mHandler is created on the mainThread and now when onDestroy is called wont it just kill the thread ? how can the handler exists after the activity is destroyed ? i have not made a new thread. Am i to understand that a handler if it has things i the message queue will remain even after a thread is destroyed ?

The reference doc im reading is here

Answer 1

Handler's are mainly used to post events to the Thread's MessageQueue.Each Handler instance is associated with a single thread and that thread's message queue.

so when you post a runnable with a delay, and exit from the activity, the MainThread will not be destroyed, as there are still events in the MessageQueue to be processed after a delay, so this can cause a memoryLeak as your anonymous innerclass of runnable is holding the reference of activity instance .

so make sure to remove all the messages in onStop() of Activity by calling

handler.removeCallbacksAndMessages(null);

this will clear all the pending message and callbacks before leaving your activity.