private void ResizeThumb_DragStarted(object sender, DragStartedEventArgs e) { parentCanvas = DesignerCanvas.FindDesignerCanvas(this); var destControl = DataContext as IBoxCanvasItem; if (parentCanvas != null && destControl != null) { var adornerLayer = AdornerLayer.GetAdornerLayer(this); if (adornerLayer != null) { Debug.Assert(sizeAdorner == null); sizeAdorner = new SizeAdorner(destControl); parentCanvas.AddAdorner(sizeAdorner); } } }