Updating UI with Runnable & postDelayed not working with timer app

Replace

mHandler.postAtTime(this, 1000);

with

mHandler.postDelayed(this, 1000);

1. You need to do UI updates in the UI thread.

2. You need to create a Handler in the UI thread to run tasks in the UI thread.

   public class MainActivity extends AppCompatActivity    private Handler mHandler;    @Override    protected void onCreate(Bundle savedInstanceState) {        mHandler = new Handler(); // This to create the Handler in the UI thread        // ...    }

This might be more along the lines of what you are looking for:

private Runnable mUpdateTimeTask = new Runnable() {       public void run() {           final long start = mStartTime;           long elapseTime = System.currentTimeMillis() - start;           int seconds = (int) (elapseTime / 1000);           int minutes = seconds / 60;           seconds     = seconds % 60;           if (seconds < 10) {               mTimeTextField.setText("" + minutes + ":0" + seconds);           } else {               mTimeTextField.setText("" + minutes + ":" + seconds);                       }           // add a delay to adjust for computation time           long delay = (1000 - (elapseTime%1000));           mHandler.postDelayed(this, delay);       }    };

I found this to be a good way to add a time to video's