flutter GestureDetector判断左滑动还是右滑动

实现这三个方法
onHorizontalDragStart:  _onHorizontalDragStart ,
onHorizontalDragUpdate: _onHorizontalDragUpdate,
onHorizontalDragEnd:  _onHorizontalDragEnd,

Offset _initialSwipeOffset;
Offset _finalSwipeOffset;

void _onHorizontalDragStart(DragStartDetails details) {
 _initialSwipeOffset = details.globalPosition;
}

void _onHorizontalDragUpdate(DragUpdateDetails details) {
 _finalSwipeOffset = details.globalPosition;
}
void _onHorizontalDragEnd(DragEndDetails details) {
 if (_initialSwipeOffset != null) {
 final offsetDifference = _initialSwipeOffset.dx - _finalSwipeOffset.dx;
 final direction = offsetDifference > 0 ? print('left') : print('right');
 }
}