public static DragAdorner Create(UIElement adornedElement, UIElement dragTarget, Point startPosition)
{
// 四角形作る
var bounds = VisualTreeHelper.GetDescendantBounds(dragTarget);
var ghost = new Rectangle()
{
Width = bounds.Width,
Height = bounds.Height,
Fill = new VisualBrush(dragTarget) { Opacity = ThisOpacity },
HorizontalAlignment = HorizontalAlignment.Left,
VerticalAlignment = VerticalAlignment.Top,
};
return new DragAdorner(adornedElement, ghost)
{
StartPosition = startPosition,
};
}