- A+
所属分类：.NET技术
一、前言
项目中涉及到了心率检测，而且数据量达到了百万级别，通过WPF实现大数据曲线图时，尝试过最基础的Canvas来实现，但是性能堪忧，而且全部画出来也不实际。同时也尝试过找第三方的开源库，但是因为曲线图涉及到很多细节功能，第三方的肯定也没法满足。没办法，只能自己实现，上网查找后发现DrawingVisual这个玩意可以实现高性能画图，同时再搭配局部显示，这样就能实现自己想要的效果。话不多说，今天把大致的实现思路写一下，就不直接把项目的源码贴出来，写个简单的Demo就好了。
二、正文
1、首先新建个项目，然后创建个自定义控件，命名为CurveChartDrawingVisual，然后让它继承FrameworkElement。因为要使用DrawingVisual对象的话，需要为它创建一个主机容器。关于其他相关DrawingVisual的细节这里不做过多阐述，不明白的可以去微软官网看。
2、实现的具体代码如下，相关细节有备注标注了。这里记得要重写一下VisualChildrenCount属性和重写GetVisualChild()方法，不然图画不出来
public class CruveChartDrawingVisual : FrameworkElement { private List<Visual> visuals = new List<Visual>(); private DrawingVisual Layer; private double offset_x = 0;//滑动条偏移值 private double y_scale;//y轴放心缩放比例 private List<int> list_points;//曲线数据 private static int Top_Val_Max = 100;//y轴最大值 private static int Top_Val_Min = 0;//y轴最小值 private static int X_Sex = 20;//x轴分度值 private static int Y_Sex = 20;//x轴分度值 private static int Bottom = 30;//底部x轴坐标显示高度 Pen pen = new Pen(Brushes.Green, 2); Pen primarygrid_pen = new Pen(Brushes.Black, 1); Pen secondgrid_pen = new Pen(Brushes.Gray, 1); public CruveChartDrawingVisual() { pen.Freeze();//冻结笔，提高性能关键所在 primarygrid_pen.Freeze(); secondgrid_pen.Freeze(); Layer = new DrawingVisual(); visuals.Add(Layer); } public void SetupData(List<int> points) { list_points = points; offset_x = 0; DrawContent(); } public void OffsetX(double offset) { offset_x = offset; DrawContent(); InvalidateVisual(); } private void DrawContent() { var dc = Layer.RenderOpen(); y_scale = (RenderSize.Height - Bottom) / (Top_Val_Max - Top_Val_Min); var mat = new Matrix(); mat.ScaleAt(1, -1, 0, RenderSize.Height / 2); mat.OffsetX = -offset_x; dc.PushTransform(new MatrixTransform(mat)); //横线 for (int y = 0; y <= Top_Val_Max - Top_Val_Min; y += 10) { Point point1 = new Point(offset_x, y * y_scale + Bottom); Point point2 = new Point(offset_x + RenderSize.Width, y * y_scale + Bottom); if (y % Y_Sex == 0) { dc.DrawLine(primarygrid_pen, point1, point2); continue; } dc.DrawLine(secondgrid_pen, point1, point2); } //竖线与文字 for (int i = 0; i <= (offset_x + RenderSize.Width); i += X_Sex * 2) { if (i < offset_x) { continue; } var point1 = new Point(i, Bottom); var point2 = new Point(i, (Top_Val_Max - Top_Val_Min) * y_scale + Bottom); //y轴文字 if (i % 100 == 0) { var text1 = new FormattedText(i + "", CultureInfo.CurrentCulture, FlowDirection.LeftToRight, new Typeface("Verdana"), 16, Brushes.Black); var mat3 = new Matrix(); mat3.ScaleAt(1, -1, i - text1.Width / 2, 8 + text1.Height / 2); dc.PushTransform(new MatrixTransform(mat3)); dc.DrawText(text1, new Point(i - text1.Width / 2, 8)); dc.Pop(); } //表格刻度文字 if (i % 100 == 0) { for (int y = Top_Val_Min; y <= Top_Val_Max; y += 10) { if (y % Y_Sex == 0) { var text1 = new FormattedText(y + "", CultureInfo.CurrentCulture, FlowDirection.LeftToRight, new Typeface("Verdana"), 12, Brushes.Black); var mat3 = new Matrix(); mat3.ScaleAt(1, -1, i + 1, (y - Top_Val_Min) * y_scale + Bottom + text1.Height / 2); dc.PushTransform(new MatrixTransform(mat3)); dc.DrawText(text1, new Point(i + 1, (y - Top_Val_Min) * y_scale + Bottom)); dc.Pop(); } } //深色竖线 dc.DrawLine(primarygrid_pen, point1, point2); continue; } //浅色竖线 dc.DrawLine(secondgrid_pen, point1, point2); } if (list_points != null) { for (int i = (int)offset_x; i < list_points.Count - 1; i++) { if (i > offset_x + RenderSize.Width) { break; } dc.DrawLine(pen, new Point(i, list_points[i] * y_scale + Bottom), new Point(i + 1, list_points[i + 1] * y_scale + Bottom)); } } dc.Pop(); dc.Close(); } protected override int VisualChildrenCount => visuals.Count; protected override Visual GetVisualChild(int index) { return visuals[index]; } protected override void OnRenderSizeChanged(SizeChangedInfo sizeInfo) { DrawContent(); base.OnRenderSizeChanged(sizeInfo); } protected override void OnRender(DrawingContext drawingContext) { drawingContext.DrawRectangle(Brushes.White, null, new Rect(0, 0, RenderSize.Width, RenderSize.Height)); base.OnRender(drawingContext); } }
3、接着测试一下，打开MainWindow，添加我们的自定义控件，这里局部显示需要搭配一个ScrollViewer来实现，代码如下
<Grid> <local:CruveChartDrawingVisual x:Name="curve" Margin="0,15,0,20" /> <ScrollViewer Name="scroll" HorizontalScrollBarVisibility="Auto" ScrollChanged="ScrollViewer_ScrollChanged" VerticalScrollBarVisibility="Disabled"> <Canvas x:Name="canvas" Height="1" /> </ScrollViewer> </Grid>
4、接着就是后台代码，比较简单，就是自动生成一个List，然后传给自定义控件，Canvas的宽度直接设置为List的长度，因为这里是水平方向一个像素点画一个点，然后滑动条滑动时再将对应的偏移值传递到控件，再通过偏移值更新视图
public partial class MainWindow : Window { private bool isAdd = true; public MainWindow() { InitializeComponent(); } private void Window_Loaded(object sender, RoutedEventArgs e) { List<int> lists = new List<int>(); int temp = 20; for (int i = 0; i < 60 * 60; i++) { if (isAdd) { lists.Add(temp); temp ++; } else { lists.Add(temp); temp --; } if (temp == 90) isAdd = false; if (temp == 10) isAdd = true; } canvas.Width = lists.Count; curve.SetupData(lists); } private void ScrollViewer_ScrollChanged(object sender, ScrollChangedEventArgs e) { curve.OffsetX(scroll.HorizontalOffset); } }
5、运行效果如下，滑动条拖到哪里就显示哪里，这样就算数据量再大也没问题
