可视化对象 DrawingVisual 使用

首先需要实例化一个DrawingVisual 对象，然后通过该对象的RenderOpen()方法获取绘图上下文DrawingContext 对象，通过该对象即可实现绘制功能，使用完后调用Close()方法关闭绘图上下文，即表示完成绘画。如果要让绘制图像在WPF元素上显示，还需要调用WPF元素对象的AddVisual(xx) 方法把可视化对象加入到元素中。

DrawingVisual visual=new DrawingVisual();
DrawingContext dc=DrawingVisual.RenderOpen();
dc.Close()

dc.DrawLine();   //画直线
dc.DrawRectangle();
dc.DrawRoundRectangle();
dc.DrawEllipse();
dc.DrawGeometry();  //画几何图形
dc.DrawText();
dc.DrawImage();
dc.DrawVideo(); //绘制视频


myPanel=new MyPanel();
DrawingVisual visual=new DrawingVisual();
using(DrawingContext dc=visual.RenderOpen())
{
     Pen drawingPen=new Pen(Brushes.Black,3);
     dc.DrawLine(drawingPen, new Point(0, 50), new Point(50, 0));
     dc.DrawLine(drawingPen, new Point(50, 0), new Point(100, 50));
     dc.DrawLine(drawingPen, new Point(0, 50), new Point(100, 50));
     dc.Close();
     myPanel.AddVisual(dv);     
}

示例：

using System.Windows;
using System.Windows.Media;

namespace WpfApp_DrawingVisual
{
    /// <summary>
    /// MainWindow.xaml 的交互逻辑
    /// </summary>
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
            Loaded += MainWindow_Loaded;
        }
        /// <summary>
        /// UIElement 中的所有元素都是继承自Visual 可视化类，DrawingVisual 也是其子类
        /// 继承关系：DrawingVisual->ContainerVisual->Visual
        /// 因此DrawingVisual 可以加入到所有的WPF 元素中，加入方法 XXX.AddVisual(),相当于在该元素上绘制图形
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        private void MainWindow_Loaded(object sender, RoutedEventArgs e)
        {
            DrawingVisual dv = new DrawingVisual();  //实例化可视化对象 
            DrawingContext dc = dv.RenderOpen();  //获取绘图上下文对象     
            Brush brush = Brushes.LightGreen;   //获取画刷对象
            Pen drawingPen = new Pen(Brushes.SteelBlue, 3);  //实例化画笔对象

            //绘制图形
            dc.DrawRectangle(brush, drawingPen, new Rect(new Point(1000,100),new Size(50,100)));
            dc.DrawEllipse(brush, drawingPen, new Point(400, 500), 200, 120);

            dc.DrawLine(drawingPen, new Point(0, 50), new Point(50, 0));
            dc.DrawLine(drawingPen, new Point(50, 0), new Point(100, 50));
            dc.DrawLine(drawingPen, new Point(0, 50), new Point(100, 50));

            dc.Close();  //关闭绘图上下文对象
            myPanel.AddVisual(dv);  //把可视化对象加入到容器myPanel中
        }
    }
}

自定义MyPanel 类 代码：

using System.Collections.Generic;
using System.Windows.Controls;
using System.Windows.Media;
namespace WpfApp_DrawingVisual
{
    public class MyPanel:Panel
    {
       private List<Visual> visuals = new List<Visual>();  //定义可视化集合对象
        protected override Visual GetVisualChild(int index)  //重写可视化对象获取方法
        {
            return visuals[index];

        }
        protected override int VisualChildrenCount => visuals.Count;  //重写可视化属性，可视化元素数量

        public void AddVisual(Visual visual) {   //添加可视化元素方法

            visuals.Add(visual); 
            base.AddLogicalChild(visual);
            base.AddVisualChild(visual);
        }  
        

    }
}

效果