GestureDragUpdateCallback onHorizontalDragUpdate

Called when the user scrolls to the left or to the right.

Source 

GestureDragUpdateCallback get onHorizontalDragUpdate => _onHorizontalDragUpdate;
void onHorizontalDragUpdate=(GestureDragUpdateCallback value)

Source 

set onHorizontalDragUpdate(GestureDragUpdateCallback value) {
  if (_onHorizontalDragUpdate == value)
    return;
  bool wasSemanticBoundary = isSemanticBoundary;
  bool hadHandler = _onHorizontalDragUpdate != null;
  _onHorizontalDragUpdate = value;
  if ((value != null) != hadHandler)
    markNeedsSemanticsUpdate(onlyChanges: isSemanticBoundary == wasSemanticBoundary);
}