ScaleGestureDetector.onTouchEvent always returns 'true'

Question

I thought that the method "onTouchEvent()" of a "ScaleGestureDetector" instance was supposed to return "true" only if it really handles the touch event, i. e. if it detects a multi-touch scaling gesture (with two fingers). Otherwise I tought that it was supposed to return "false" in order to let other handlers handle the event, e. g. a long press for triggering a context menu.

I observed something different: scaleGestureDetector.onTouchEvent() always returns "true" in my case. The following code snippet of my MyView class:

public boolean onTouchEvent(MotionEvent event) {
  boolean retval = scaleGestureDetector.onTouchEvent(event);
   Log.v("MyView.onTouchEvent()", "Action: " + event.getAction() +
         "; PointerCount: " + event.getPointerCount() +
         "; scaleGestureDetector.onTouchEvent() RetVal: " + retval);
   return(retval);
}

produced the follwing log output after I touched the view for approx 1 second with one finger, then performed a scale gesture with 2 fingers:

01-01 19:09:54.484: VERBOSE/MyView.onTouchEvent()(5930): Action: 0; PointerCount: 1; scaleGestureDetector.onTouchEvent() RetVal: true
01-01 19:09:54.510: VERBOSE/MyView.onTouchEvent()(5930): Action: 2; PointerCount: 1; scaleGestureDetector.onTouchEvent() RetVal: true
01-01 19:09:54.541: VERBOSE/MyView.onTouchEvent()(5930): Action: 2; PointerCount: 1; scaleGestureDetector.onTouchEvent() RetVal: true
01-01 19:09:54.580: VERBOSE/MyView.onTouchEvent()(5930): Action: 2; PointerCount: 1; scaleGestureDetector.onTouchEvent() RetVal: true
01-01 19:09:54.820: VERBOSE/MyView.onTouchEvent()(5930): Action: 2; PointerCount: 1; scaleGestureDetector.onTouchEvent() RetVal: true
01-01 19:09:54.910: VERBOSE/MyView.onTouchEvent()(5930): Action: 2; PointerCount: 1; scaleGestureDetector.onTouchEvent() RetVal: true
01-01 19:09:55.050: VERBOSE/MyView.onTouchEvent()(5930): Action: 2; PointerCount: 1; scaleGestureDetector.onTouchEvent() RetVal: true
01-01 19:09:55.350: VERBOSE/MyView.onTouchEvent()(5930): Action: 2; PointerCount: 1; scaleGestureDetector.onTouchEvent() RetVal: true
01-01 19:09:55.400: VERBOSE/MyView.onTouchEvent()(5930): Action: 1; PointerCount: 1; scaleGestureDetector.onTouchEvent() RetVal: true
01-01 19:09:57.160: INFO/BatteryStatsImpl(96): notePhoneSignalStrengthLocked: 4->3
01-01 19:10:00.060: ERROR/ClockWidget(215): weatherClock onReceive~ mUseAnimation:false
01-01 19:10:00.060: ERROR/ClockWidget(215): handleUiMessage~ in pause. msg:36867
01-01 19:10:00.070: ERROR/ClockWidget(215): weatherClock onReceive~ mUseAnimation:false
01-01 19:10:00.090: INFO/PI.Alarms(699): Update Alarms start
01-01 19:10:00.090: INFO/PI.Alarms(699): Task Notifications: Already displaying the same alarms, no update
01-01 19:10:00.100: INFO/PI.Alarms(699): Event Notifications: Already displaying the same alarms, no update
01-01 19:10:00.830: VERBOSE/MyView.onTouchEvent()(5930): Action: 0; PointerCount: 1; scaleGestureDetector.onTouchEvent() RetVal: true
01-01 19:10:00.840: VERBOSE/MyView.onTouchEvent()(5930): Action: 2; PointerCount: 1; scaleGestureDetector.onTouchEvent() RetVal: true
01-01 19:10:00.870: VERBOSE/MyView.onTouchEvent()(5930): Action: 2; PointerCount: 1; scaleGestureDetector.onTouchEvent() RetVal: true
01-01 19:10:00.900: VERBOSE/MyView.onTouchEvent()(5930): Action: 2; PointerCount: 1; scaleGestureDetector.onTouchEvent() RetVal: true
01-01 19:10:00.922: VERBOSE/MyView.onTouchEvent()(5930): Action: 2; PointerCount: 1; scaleGestureDetector.onTouchEvent() RetVal: true
01-01 19:10:00.931: VERBOSE/MyView.onTouchEvent()(5930): Action: 261; PointerCount: 2; scaleGestureDetector.onTouchEvent() RetVal: true
01-01 19:10:00.950: VERBOSE/MyView.onTouchEvent()(5930): Action: 2; PointerCount: 2; scaleGestureDetector.onTouchEvent() RetVal: true
01-01 19:10:01.002: VERBOSE/MyView.onTouchEvent()(5930): Action: 2; PointerCount: 2; scaleGestureDetector.onTouchEvent() RetVal: true
01-01 19:10:01.030: VERBOSE/MyView.onTouchEvent()(5930): Action: 2; PointerCount: 2; scaleGestureDetector.onTouchEvent() RetVal: true
01-01 19:10:01.060: VERBOSE/MyView.onTouchEvent()(5930): Action: 2; PointerCount: 2; scaleGestureDetector.onTouchEvent() RetVal: true
01-01 19:10:01.090: VERBOSE/MyView.onTouchEvent()(5930): Action: 2; PointerCount: 2; scaleGestureDetector.onTouchEvent() RetVal: true
01-01 19:10:01.120: VERBOSE/MyView.onTouchEvent()(5930): Action: 2; PointerCount: 2; scaleGestureDetector.onTouchEvent() RetVal: true
01-01 19:10:01.140: VERBOSE/MyView.onTouchEvent()(5930): Action: 2; PointerCount: 2; scaleGestureDetector.onTouchEvent() RetVal: true
01-01 19:10:01.172: VERBOSE/MyView.onTouchEvent()(5930): Action: 2; PointerCount: 2; scaleGestureDetector.onTouchEvent() RetVal: true
01-01 19:10:01.200: VERBOSE/MyView.onTouchEvent()(5930): Action: 2; PointerCount: 2; scaleGestureDetector.onTouchEvent() RetVal: true
01-01 19:10:01.230: VERBOSE/MyView.onTouchEvent()(5930): Action: 2; PointerCount: 2; scaleGestureDetector.onTouchEvent() RetVal: true
01-01 19:10:01.252: VERBOSE/MyView.onTouchEvent()(5930): Action: 2; PointerCount: 2; scaleGestureDetector.onTouchEvent() RetVal: true
01-01 19:10:01.280: VERBOSE/MyView.onTouchEvent()(5930): Action: 2; PointerCount: 2; scaleGestureDetector.onTouchEvent() RetVal: true
01-01 19:10:01.310: VERBOSE/MyView.onTouchEvent()(5930): Action: 2; PointerCount: 2; scaleGestureDetector.onTouchEvent() RetVal: true
01-01 19:10:01.342: VERBOSE/MyView.onTouchEvent()(5930): Action: 2; PointerCount: 2; scaleGestureDetector.onTouchEvent() RetVal: true
01-01 19:10:01.370: VERBOSE/MyView.onTouchEvent()(5930): Action: 2; PointerCount: 2; scaleGestureDetector.onTouchEvent() RetVal: true
01-01 19:10:01.390: VERBOSE/MyView.onTouchEvent()(5930): Action: 2; PointerCount: 2; scaleGestureDetector.onTouchEvent() RetVal: true
01-01 19:10:01.424: VERBOSE/MyView.onTouchEvent()(5930): Action: 2; PointerCount: 2; scaleGestureDetector.onTouchEvent() RetVal: true
01-01 19:10:01.450: VERBOSE/MyView.onTouchEvent()(5930): Action: 2; PointerCount: 2; scaleGestureDetector.onTouchEvent() RetVal: true
01-01 19:10:01.480: VERBOSE/MyView.onTouchEvent()(5930): Action: 2; PointerCount: 2; scaleGestureDetector.onTouchEvent() RetVal: true
01-01 19:10:01.510: VERBOSE/MyView.onTouchEvent()(5930): Action: 2; PointerCount: 2; scaleGestureDetector.onTouchEvent() RetVal: true
01-01 19:10:01.530: VERBOSE/MyView.onTouchEvent()(5930): Action: 2; PointerCount: 2; scaleGestureDetector.onTouchEvent() RetVal: true
01-01 19:10:01.580: VERBOSE/MyView.onTouchEvent()(5930): Action: 2; PointerCount: 2; scaleGestureDetector.onTouchEvent() RetVal: true
01-01 19:10:01.690: VERBOSE/MyView.onTouchEvent()(5930): Action: 2; PointerCount: 2; scaleGestureDetector.onTouchEvent() RetVal: true
01-01 19:10:01.780: VERBOSE/MyView.onTouchEvent()(5930): Action: 2; PointerCount: 2; scaleGestureDetector.onTouchEvent() RetVal: true
01-01 19:10:01.815: VERBOSE/MyView.onTouchEvent()(5930): Action: 2; PointerCount: 2; scaleGestureDetector.onTouchEvent() RetVal: true
01-01 19:10:01.830: VERBOSE/MyView.onTouchEvent()(5930): Action: 262; PointerCount: 2; scaleGestureDetector.onTouchEvent() RetVal: true
01-01 19:10:01.840: VERBOSE/MyView.onTouchEvent()(5930): Action: 1; PointerCount: 1; scaleGestureDetector.onTouchEvent() RetVal: true

As I said: The return value is always "true"! Is this a bug of ScaleGestureDetector.onTouchEvent()? What can I do to let other handlers handle all non-scale-gesture events (e. g. long press with 1 finger)? Please help!

Nemax

Answer 1

Don't know if it's a bug or intentional, but that's definitely what the source does (ScaleGestureDetector.java:156):

public boolean onTouchEvent(MotionEvent event) {
   final int action = event.getAction();
   boolean handled = true;

   /* ... bunch of code that never updates 'handled' */

   return handled;
}

The way I solved this was to check all of the other types of touch events I might want to handle first, then invoke the gesture detector, e.g.

    if (mLongPressGestureDetector != null && mLongPressGestureDetector.onTouchEvent(event))
        return true;
    else if (mIsInMoveMode && mScaleGestureDetector != null) {
        // Check for a move
        if (action == MotionEvent.ACTION_MOVE && !mScaleGestureDetector.isInProgress()) {
            handleMove(event);
            return true;
        }

        // Now a scale
        mScaleGestureDetector.onTouchEvent(event);
        return true;
    }