onResizeR method

Implementation

onResizeR(DragUpdateDetails details)
{
  if (widget.model.resizeable == false) return;
  if (((width  ?? 0) + details.delta.dx) < minimumSize) return;
  setState(()
  {
    width  = (width  ?? 0) + details.delta.dx;
    lastDx     = dx;
    lastWidth  = width;
  });
}