'宣言 Protected Overridable Sub GetVisibleItems( _ ByVal windowRect As Rect, _ ByVal viewportRect As Rect, _ ByVal itemLocations As IList(Of Point), _ ByVal visibleItems As List(Of Integer) _ )
protected virtual void GetVisibleItems( Rect windowRect, Rect viewportRect, IList<Point> itemLocations, List<int> visibleItems )