public override void OnApplyTemplate()
        {
            _leftThumb = base.GetTemplateChild("PART_LeftThumb") as Thumb ?? new Thumb();
            _rightThumb = base.GetTemplateChild("PART_RightThumb") as Thumb ?? new Thumb();

            _leftThumb.SetBinding(Canvas.LeftProperty, new Binding("LeftThumbPos") { Source = this });
            _rightThumb.SetBinding(Canvas.RightProperty, new Binding("RightThumbPos") { Source = this });

            _leftThumb.DragDelta += DragDeltaLeft;
            _rightThumb.DragDelta += DragDeltaRight;

            base.OnApplyTemplate();
        }