在我们实际的工作中可能经常使用到圆形的进度条，但是这是怎么实现的呢？其实这只不过是修改了一下ProgressBar的模板，我们在下面的代码中我们将ProgressBar的Value值绑定到Border的Background上面，并且使用了一个ValueToProcessConverter的转换器进行相应地转换，这里重点介绍一下这个转换器

<ProgressBar Name="pb" Minimum="0" Maximum="100" > <ProgressBar.Template> <ControlTemplate TargetType="ProgressBar"> <Border Background="{TemplateBinding Value, Converter={StaticResource ValueToProcessConverter}, ConverterParameter=250}"/> </ControlTemplate> </ProgressBar.Template></ProgressBar>

下面介绍这部分的源码，并做简要的分析：

首先，获取ProgressBar.Value，然后再获取ConverterParameter=250这个值，通过这两个值就能确定画的圆环的大小和ProgressBar显示的值，然后我们再调用DrawBrush(arg, 100, radius, radius, Thickness)这个函数来进行绘制，具体代码如下：

private Brush DrawBrush(double value, double maxValue, double radiusX, double radiusY, double thickness){DrawingGroup drawingGroup = new DrawingGroup();DrawingContext drawingContext = drawingGroup.Open();DrawingGeometry(drawingContext, value, maxValue, radiusX, radiusY, thickness);DrawingBrush brush = new DrawingBrush(drawingGroup);return brush;}

　　这里需要注意的是绝不能直接实例化DrawingContext；但可以通过某些方法（例如DrawingGroup.Open和DrawingVisual.RenderOpen）获取绘图上下文。我们这里是使用DrawingGroup.Open的方法来进行相应的绘图，然后在里面调用里DrawingGeometry这个函数，在这个函数中开始绘制一些DrawEllipse和DrawGeometry，在这个函数中我们讲解一下FormattedText 这个类，使用FormattedText对象可以绘制多行文本，且可以单独对该文本中的每个字符设置格式。

private void DrawingGeometry(DrawingContext drawingContext, double value, double maxValue, double radiusX, double radiusY, double thickness){drawingContext.DrawEllipse(null, new Pen(EllipseBrush, thickness), centerPoint, radiusX, radiusY);drawingContext.DrawGeometry(NormalBrush, new Pen(), GetGeometry(value, maxValue, radiusX, radiusY, thickness));FormattedText formatWords = new FormattedText(percentString, CultureInfo.CurrentCulture, FlowDirection.LeftToRight, SuccessRateTypeface, SuccessRateFontSize, NormalBrush);Point startPoint = new Point(centerPoint.X - formatWords.Width / 2, centerPoint.Y - formatWords.Height / 2 - SuccessRateFontCorrectionValue);drawingContext.DrawText(formatWords, startPoint);drawingContext.Close();}　　public class ValueToProcessConverter : IValueConverter{readonly double Thickness = 20;private Point centerPoint;private double radius;readonly SolidColorBrush NormalBrush = new SolidColorBrush(Colors.White);readonly SolidColorBrush EllipseBrush = new SolidColorBrush(Color.FromRgb(107, 132, 165));string percentString;private static readonly Typeface SuccessRateTypeface;private const int SuccessRateFontSize = 65;readonly double SuccessRateFontCorrectionValue = 12;static ValueToProcessConverter(){SuccessRateTypeface = new Typeface(new FontFamily("MSYH"), new FontStyle(), new FontWeight(), new FontStretch());}public ValueToProcessConverter(){}public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture){if (value is double && !string.IsNullOrEmpty((string)parameter)){double arg = (double)value;double width = double.Parse((string)parameter);radius = width / 2;centerPoint = new Point(radius, radius);return DrawBrush(arg, 100, radius, radius, Thickness);}else{throw new ArgumentException();}}public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture){throw new NotImplementedException();}/// <summary>/// 根据角度获取坐标/// </summary>/// <param name="CenterPoint"></param>/// <param name="r"></param>/// <param name="angel"></param>/// <returns></returns>private Point GetPointByAngel(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;}/// <summary>/// 根据4个坐标画出扇形/// </summary>/// <param name="bigFirstPoint"></param>/// <param name="bigSecondPoint"></param>/// <param name="smallFirstPoint"></param>/// <param name="smallSecondPoint"></param>/// <param name="bigRadius"></param>/// <param name="smallRadius"></param>/// <param name="isLargeArc"></param>/// <returns></returns>private Geometry DrawingArcGeometry(Point bigFirstPoint, Point bigSecondPoint, Point smallFirstPoint, Point smallSecondPoint, double bigRadius, double smallRadius, bool isLargeArc){PathFigure pathFigure = new PathFigure { IsClosed = true };pathFigure.StartPoint = bigFirstPoint;pathFigure.Segments.Add(new ArcSegment{Point = bigSecondPoint,IsLargeArc = isLargeArc,Size = new Size(bigRadius, bigRadius),SweepDirection = SweepDirection.Clockwise});pathFigure.Segments.Add(new LineSegment { Point = smallSecondPoint });pathFigure.Segments.Add(new ArcSegment{Point = smallFirstPoint,IsLargeArc = isLargeArc,Size = new Size(smallRadius, smallRadius),SweepDirection = SweepDirection.Counterclockwise});PathGeometry pathGeometry = new PathGeometry();pathGeometry.Figures.Add(pathFigure);return pathGeometry;}/// <summary>/// 根据当前值和最大值获取扇形/// </summary>/// <param name="value"></param>/// <param name="maxValue"></param>/// <returns></returns>private Geometry GetGeometry(double value, double maxValue, double radiusX, double radiusY, double thickness){bool isLargeArc = false;double percent = value / maxValue;percentString = string.Format("{0}%", Math.Round(percent * 100, 2));double angel = percent * 360D;if (angel > 180) isLargeArc = true;double bigR = radiusX + thickness / 2;double smallR = radiusX - thickness / 2;Point firstpoint = GetPointByAngel(centerPoint, bigR, 0);Point secondpoint = GetPointByAngel(centerPoint, bigR, angel);Point thirdpoint = GetPointByAngel(centerPoint, smallR, 0);Point fourpoint = GetPointByAngel(centerPoint, smallR, angel);return DrawingArcGeometry(firstpoint, secondpoint, thirdpoint, fourpoint, bigR, smallR, isLargeArc);}/// <summary>/// 画扇形/// </summary>/// <param name="drawingContext"></param>/// <param name="value"></param>/// <param name="maxValue"></param>/// <param name="radiusX"></param>/// <param name="radiusY"></param>/// <param name="thickness"></param>private void DrawingGeometry(DrawingContext drawingContext, double value, double maxValue, double radiusX, double radiusY, double thickness){drawingContext.DrawEllipse(null, new Pen(EllipseBrush, thickness), centerPoint, radiusX, radiusY);drawingContext.DrawGeometry(NormalBrush, new Pen(), GetGeometry(value, maxValue, radiusX, radiusY, thickness));FormattedText formatWords = new FormattedText(percentString, CultureInfo.CurrentCulture, FlowDirection.LeftToRight, SuccessRateTypeface, SuccessRateFontSize, NormalBrush);Point startPoint = new Point(centerPoint.X - formatWords.Width / 2, centerPoint.Y - formatWords.Height / 2 - SuccessRateFontCorrectionValue);drawingContext.DrawText(formatWords, startPoint);drawingContext.Close();}/// <summary>/// 根据当前值和最大值画出进度条/// </summary>/// <param name="value"></param>/// <param name="maxValue"></param>/// <returns></returns>private Brush DrawBrush(double value, double maxValue, double radiusX, double radiusY, double thickness){DrawingGroup drawingGroup = new DrawingGroup();DrawingContext drawingContext = drawingGroup.Open();DrawingGeometry(drawingContext, value, maxValue, radiusX, radiusY, thickness);DrawingBrush brush = new DrawingBrush(drawingGroup);return brush;}}

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