WPF InkCanvas

Question

现在使用

 /// <summary>
        /// 画扇形
        /// </summary>
        /// <param name="point">圆心</param>
        /// <param name="wedgeAngle">角度</param>
        /// <param name="radius">半径</param>
        /// <param name="rotateAngle">整体旋转角度</param>
        /// <returns></returns>
        protected Geometry DefiningGeometry(Point point, double wedgeAngle, double radius, double rotateAngle,bool isLarge)
        {
            StreamGeometry geometry = new StreamGeometry();
            geometry.FillRule = FillRule.EvenOdd;

            using (StreamGeometryContext context = geometry.Open())
            {
                Point outerArcStartPoint = ComputeCartesianCoordinate(90.0 + rotateAngle, radius);
                outerArcStartPoint.Offset(point.X, point.Y);

                Point outerArcEndPoint = ComputeCartesianCoordinate(90.0 + wedgeAngle + rotateAngle, radius);
                outerArcEndPoint.Offset(point.X, point.Y);

                bool largeArc = wedgeAngle > 180.0;

                Size outerArcSize = new Size(radius, radius);
                DrawGeometry(context, point, outerArcStartPoint, outerArcEndPoint, outerArcSize, largeArc,isLarge);
            }

            geometry.Freeze();
            return geometry;
        }

        /// <summary>
        /// 扇形画法
        /// </summary>
        protected virtual void DrawGeometry(StreamGeometryContext context, Point innerStartPoint, Point outerStartPoint, Point outerEndPoint, Size outerSize, bool largeArc, bool isLarge)
        {        
            context.BeginFigure(innerStartPoint, true, true);
            context.LineTo(outerStartPoint, true, true);
            context.ArcTo(outerEndPoint, outerSize, 0, largeArc, SweepDirection.Clockwise, true, true);
            context.LineTo(innerStartPoint, true, true);
        }

        /// <summary>
        /// Converts a coordinate from the polar coordinate system to the cartesian coordinate system.
        /// </summary>
        public Point ComputeCartesianCoordinate(double angle, double radius)
        {
            double angleRad = (Math.PI / 180.0) * (angle - 90);

            double x = radius * Math.Cos(angleRad);
            double y = radius * Math.Sin(angleRad);

            return new Point(x, y);
        }

绘制一个Geometry ，并通过InkCanvas的

protected override void DrawCore(DrawingContext drawingContext, DrawingAttributes drawingAttributes)

{

drawingContext.DrawGeometry(
                null,
                GetPen(GUIDConst.LineColor, GUIDConst.LineThickness),//画笔
                上面绘制的Geometry );

}，可以显示，但InkCanvas选中拖动效果就没有了，请问如何解决