在DrawingVisual上绘制圆形的进度条，类似于IOS系统风格。

1.说明：在WPF中，文件下载时需要显示下载进度，由于系统自带的条型进度条比较占用空间，改用圆形的进度条,需要在DrawingVisual上呈现。

运行的效果如图：

               private Point GetPointOnCir(Point CenterPoint, double r, double angel)
               {
                       Point p = new Point();
                       p.X = Math.Sin(angel * Math.PI / 180) * r + CenterPoint.X;
                       p.Y = CenterPoint.Y - Math.Cos(angel * Math.PI / 180) * r;
                       return p;
               }
               private Geometry drawingArc(Point bigCirclefirstPoint, Point bigCirclesecondPoint, Point smallCirclefirstPoint, Point smallCirclesecondPoint, double bigCircleRadius, double smallCircleRadius,bool  isLargeArc)
               {
                       PathFigure pathFigure = new PathFigure { IsClosed = true };
                       pathFigure.StartPoint = bigCirclefirstPoint;
                       pathFigure.Segments.Add(
                         new ArcSegment
                         {
                                 Point = bigCirclesecondPoint,
                                 IsLargeArc = isLargeArc,
                                 Size = new Size(bigCircleRadius, bigCircleRadius),
                                 SweepDirection = SweepDirection.Clockwise
                         });
                       pathFigure.Segments.Add(new LineSegment { Point = smallCirclesecondPoint });
                       pathFigure.Segments.Add(
                        new ArcSegment
                        {
                                Point = smallCirclefirstPoint,
                                IsLargeArc = isLargeArc,
                                Size = new Size(smallCircleRadius, smallCircleRadius),
                                SweepDirection = SweepDirection.Counterclockwise
                        });
                       PathGeometry pathGeometry = new PathGeometry();
                       pathGeometry.Figures.Add(pathFigure);
                       return pathGeometry;
               }
               //根据已保存的大小和文件总大小来计算下载进度百分比
                  private Geometry GetGeometry()
                {
                        bool isLargeArc =false;
                        double percent = double.Parse(Convert.ToString(savedSize)) / double.Parse(Convert.ToString(fileSize));
                        PercentString = string.Format("{0}%",Math.Round(percent*100,0));
                        double angel = percent * 360D;
                        if(angel>180)isLargeArc=true;
                        //double angel = 45;
                        double bigR = 16;
                        double smallR = 13;
                        Point centerPoint = vl.StartPoint;//new Point(100, 300);
                        Point firstpoint = GetPointOnCir(centerPoint, bigR, 0);
                        Point secondpoint = GetPointOnCir(centerPoint, bigR, angel);
                        Point thirdpoint = GetPointOnCir(centerPoint, smallR, 0);
                        Point fourpoint = GetPointOnCir(centerPoint, smallR, angel);
                        return drawingArc(firstp, secondpoint, thirdpoint, fourpoint, bigR, smallR, isLargeArc);
                }

画圆形的进度条，实际上是动态画两个同心圆，根据文件保存的百分比来计算画弧形的角度的大小，需要7个参数：大圆的半径bigR 、小圆的半径smallR 、同心圆的圆心centerPoint 、大圆的起始点firstpoint 、大圆的结束点secondpoint 、小圆的起始点thirdpoint、小圆的结束点fourpoint

最后需要使用DrawingContext把圆给画出来：

                public Visual drawShape()
                {
                        DrawingVisual drawingWordsVisual = new DrawingVisual();
                        DrawingContext drawingContext = drawingWordsVisual.RenderOpen();
                        try
                        {
                                if (savedSize != fileSize)
                                {

                                        drawingContext.DrawEllipse(null, new Pen(Brushes.Gray, 3), vl.StartPoint, 13, 13);
                                        drawingContext.DrawGeometry(vs.VisualBackgroundBrush, vs.VisualFramePen, GetGeometry());
                                        FormattedText formatWords = new FormattedText(PercentString, System.Globalization.CultureInfo.CurrentCulture, FlowDirection.LeftToRight, new Typeface(vs.WordsFont.Name), vs.WordsFont.Size, currentStyle.VisualBackgroundBrush);
                                        formatWords.SetFontWeight(FontWeights.Bold);
                                        Point startPoint = new Point(vl.StartPoint.X - formatWords.Width / 2, vl.StartPoint.Y - formatWords.Height / 2);
                                        drawingContext.DrawText(formatWords, startPoint);
                                }
                                else
                                {
                                        drawingContext.DrawEllipse(null, new Pen(Brushes.Green, 3), vl.StartPoint, 16, 16);
                                        FormattedText formatWords = new FormattedText("Open", System.Globalization.CultureInfo.CurrentCulture, FlowDirection.LeftToRight, new Typeface(vs.WordsFont.Name), vs.WordsFont.Size, Brushes.Red);
                                        formatWords.SetFontWeight(FontWeights.Bold);
                                        Point startPoint = new Point(vl.StartPoint.X - formatWords.Width / 2, vl.StartPoint.Y - formatWords.Height / 2);
                                        drawingContext.DrawText(formatWords, startPoint);
                                }

                        }
                        catch (Exception ex)
                        {
                                new SaveExceptionInfo().SaveLogAsTXTInfoex(ex.Message);
                        }
                        finally
                        {
                                drawingContext.Close();
                        }
                        return drawingWordsVisual;
                }