如何实现圆形的进度条(ProgressBar)

      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;
        }

    }