1. override
void acceptGesture(int pointer)

Called when this member wins the arena for the given pointer id.

Source 

@override
void acceptGesture(int pointer) {
  if (_state != _DragState.accepted) {
    _state = _DragState.accepted;
    Offset delta = _pendingDragOffset;
    _pendingDragOffset = Offset.zero;
    if (onStart != null)
      invokeCallback/*<Null>*/('onStart', () => onStart(new DragStartDetails(globalPosition: _initialPosition))); // ignore: STRONG_MODE_INVALID_CAST_FUNCTION_EXPR, https://github.com/dart-lang/sdk/issues/27504
    if (delta != Offset.zero && onUpdate != null) {
      invokeCallback/*<Null>*/('onUpdate', () => onUpdate(new DragUpdateDetails( // ignore: STRONG_MODE_INVALID_CAST_FUNCTION_EXPR, https://github.com/dart-lang/sdk/issues/27504
        delta: _getDeltaForDetails(delta),
        primaryDelta: _getPrimaryDeltaForDetails(delta)
      )));
    }
  }
}