drag method
Start a drag activity corresponding to the given DragStartDetails.
The onDragCanceled argument will be invoked if the drag is ended
prematurely (e.g. from another activity taking over). See
ScrollDragController.onDragCanceled for details.
Implementation
@override
Drag drag(DragStartDetails details, VoidCallback dragCancelCallback) {
throw UnimplementedError();
}