onResizeT method

Implementation

onResizeT(DragUpdateDetails details)
{
  if (widget.model.resizeable == false) return;
  if (((height ?? 0) - details.delta.dy) < minimumSize) return;
  setState(()
  {
    height = (height ?? 0) - details.delta.dy;
    dy = dy! + details.delta.dy;
    lastDy     = dy;
    lastHeight = height;
  });
}