onInterceptTouchEvent never receives action_move

Question

I have a custom ViewGroup with an override of onInterceptTouchEvent(). It receives ACTION_DOWN but never receives ACTION_MOVE. It is my understanding that, unless it returns "true", it should receive all MotionEvents.

The ViewGroup contains two views, an ImageView and a GridLayout.

My intercept code is:

  @Override
  public boolean onInterceptTouchEvent(MotionEvent ev)
  {
    final int action = ev.getAction();
    switch (action & MotionEvent.ACTION_MASK)
    {
      case MotionEvent.ACTION_DOWN:
        logD ("DDV Intercept DOWN");
        break;
      case MotionEvent.ACTION_POINTER_DOWN:
        logD ("DDV Intercept P DOWN"); // logD: shell around Log.d()
        break;
      case MotionEvent.ACTION_MOVE:
        logD ("DDV Intercept MOVE");
        break;
      case MotionEvent.ACTION_UP:
        logD ("DDV Intercept UP");
        break;
      case MotionEvent.ACTION_POINTER_UP:
        logD ("DDV Intercept P UP " + ev.getActionIndex());
        break;
      case MotionEvent.ACTION_CANCEL: 
        logD ("DDV Intercept CANCEL");
        break;
      default:
        logD ("DDV Intercept " + (action & MotionEvent.ACTION_MASK));
    }        
    return false;
  }

I also have code for onTouch that returns false except for one case in ACTION_MOVE; however, it's called only for ACTION_DOWN is called; thus it only return false.

Answer 1

It's a bit more complicated than that. First of all you need to override onTouchEvent() and handle ACTION_DOWN and MOVE events there too. Then the following will happen.

1. ACTION_DOWN event gets dispatched to onInterceptTouchEvent() first. You should return false from there.
2. Now there are two cases:
   • If there is no touchable view underneath ACTION_DONW event's location in the view tree, then ACTION_DOWN event and all follow up events get dispatched to onTouchEvent(). You must return true from there. Only then you will receive follow up events sent to onTouchEvent() method. Independently on whether you return true or false, onInterceptTouchEvent() will not receive any follow up events anymore.
   • If there is a touchable view, then all events will be dispatched to onInterceptTouchEvent() (including ACTION_MOVE events). You need to return true from there, after you detected your gesture. Once you return true from here, touchable view will receive ACTION_CANCEL event and all further events will be dispatched to onTouchEvent() method.

Hope this helps.