Question

I have a game app which is mostly working fine. If a phone call comes in during the game (and I am not currently touching the screen) then the game copes with the subsequent onPause and onResume exactly as I would expect and it carriese on from where it left off. However if I am touching the screen at the moment the call comes in the program crashes. Logcat reports a NullPointerException at the line synchronized (micks_thread_thing.getSurfaceHolder()). I presume that sometimes the getSurfaceHolder can fail, but I’m not sure how I could have written the code differently to avoid the error.

    public boolean onTouchEvent(MotionEvent event) 
    {
      super.onTouchEvent(event); // not sure if I need this

      synchronized (micks_thread_thing.getSurfaceHolder()) // this is the line causing the nullpointerexception
      {
        if (event.getAction() == MotionEvent.ACTION_DOWN) 
        {
          do_down(event.getX(),event.getY());
        }
        if (event.getAction() == MotionEvent.ACTION_MOVE) 
        {
          do_move(event.getX(),event.getY());
        }

        if (event.getAction() == MotionEvent.ACTION_UP) 
        {
          do_up(event.getX(),event.getY());
        }
      }
      return true;
    }

Answer 1

try wrapping your entire synchronized block in a null check on your thread:

if(micks_thread_thing != null) 
{
synchronized (micks_thread_thing.getSurfaceHolder()) // this is the line causing the nullpointerexception
  {
    if (event.getAction() == MotionEvent.ACTION_DOWN) 
    {
      do_down(event.getX(),event.getY());
    }
    if (event.getAction() == MotionEvent.ACTION_MOVE) 
    {
      do_move(event.getX(),event.getY());
    }

    if (event.getAction() == MotionEvent.ACTION_UP) 
    {
      do_up(event.getX(),event.getY());
    }
  }
}