Java handlerthread is not running in the background?

I'm trying to learn how to use handlerthread to run things in the background. I have a button in the clip. When I click this button, I want to get the number of entries from the database. But when I actually run it, logcat says that the application may do too much work on the main thread, and I don't know what I've done wrong

This is how I arrange the code in the fragment:

private Handler handler=new Handler();
private MyWorkerThread myWorkerThread;

private Runnable myRunnable=new Runnable() {
    @Override
    public void run() {
        handler.post(new Runnable() {
            @Override
            public void run() {
                List<Item> list=db.getAllItems();
                Log.d(TAG,"Size: "+list.size());
            }
        });
    }
};

private class MyWorkerThread extends HandlerThread{
    private Handler myHandler;

    private MyWorkerThread(String name) {
        super(name);
    }

    private void postTask(Runnable task){
        myHandler.post(task);
    }

    private void setMyHandler(){
        myHandler=new Handler(getLooper());
    }
}

@Override
public void onCreate(@Nullable Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    myWorkerThread=new MyWorkerThread("myWorkerThread");
    myWorkerThread.start();
    myWorkerThread.setMyHandler();
}

@OnClick(R.id.btn)
void getCount(){
    myWorkerThread.postTask(myRunnable);
}

I'm following the example in this blog post, but I'm not sure what I did wrong, and it still blocks the UI at run time

resolvent:

Remove it from your runnable:

handler.post(new Runnable() {

You are publishing your runnable, which sends it back to the main thread. Therefore, your main thread is still performing all work