onVerticalDragUpdate property Null safety

GestureDragUpdateCallback? onVerticalDragUpdate

Called when the user scrolls up or down.

Implementation

GestureDragUpdateCallback? get onVerticalDragUpdate => _onVerticalDragUpdate;
void onVerticalDragUpdate=(GestureDragUpdateCallback? value)

Implementation

set onVerticalDragUpdate(GestureDragUpdateCallback? value) {
  if (_onVerticalDragUpdate == value)
    return;
  final bool hadHandler = _onVerticalDragUpdate != null;
  _onVerticalDragUpdate = value;
  if ((value != null) != hadHandler)
    markNeedsSemanticsUpdate();
}