Flutter: Gesture recognizer hanldes multiple taps, then draggable, useful for map dragging, image scaling (with example)

multi_taps_to_pan_gesture_recognizer.dart

class MultiTapsToPanGestureRecognizer extends TapAndPanGestureRecognizer {
  var minTapsToDrag = 1;
  var timeoutToTaps = const Duration(milliseconds: 200);

  @protected
  var canDrag = false;
  @protected
  var firedDrag = false;
  @protected
  var firstTapms = 0;
  @protected
  var tapsBeforeTimeout = 0;

  @protected
  reset() {
    firstTapms = 0;
    tapsBeforeTimeout = 0;
    canDrag = false;
    firedDrag = false;
  }

  @override
  void acceptGesture(int pointer) {
    super.acceptGesture(pointer);

    if (currentDown != null) {
      final nowms = DateTime.now().millisecondsSinceEpoch;
      final firstTapms = this.firstTapms;
      if (nowms - firstTapms > timeoutToTaps.inMilliseconds) {
        reset();
        this.firstTapms = nowms;
        tapsBeforeTimeout = 1;
      } else {
        tapsBeforeTimeout++;
      }
    }

    if (tapsBeforeTimeout >= minTapsToDrag) {
      tapsBeforeTimeout = 0;
      firstTapms = 0;
      canDrag = true;
    }

    if (currentUp != null && firedDrag) {
      reset();
    }
  }

  @override
  void handleEvent(PointerEvent event) {
    if (event is PointerMoveEvent) {
      if (canDrag) {
        firedDrag = true;
        super.handleEvent(event);
      }
    } else {
      super.handleEvent(event);
    }
  }
}

multi_taps_to_pan_gesture_recognizer_example.dart

/// tap at least 2 times in 500ms, then drag
/// fires:
/// - on tap down in 2 times
/// - on drag start
/// - on drag update
Widget example() {
  return RawGestureDetector(
    behavior: HitTestBehavior.opaque,
    gestures: {
      MultiTapsToPanGestureRecognizer: GestureRecognizerFactoryWithHandlers<MultiTapsToPanGestureRecognizer>(
        () => MultiTapsToPanGestureRecognizer(),
        (recognizer) { 
          // configure handlers with
          recognizer
            // no slop
            ..gestureSettings = const DeviceGestureSettings(touchSlop: 0)
            // tap at least 2 times, then draggable
            ..minTapsToDrag = 2 
            ..onTapDown = (e) {}
            ..onDragUpdate = (e) {}
            ..onDragEnd = (e) {}
            ..onCancel = () {}
        }
      ),
    }
  );
}