命中测试HitTestResult

命中测试：是指某点是否在目标元素范围之内

//返回点击目标 即命中测试结果对象
HitTestResult hitTestResult=VisualTreeHelper.HitTest(this,point);
hitTestResult.VisualHit as DrawingVisual;  //命中目标封装在命中测试的VisualHit 中，这个
属性的类型时DependencyObject 即依赖对象，因此这里需要转换成 DrawingVisual类型

示例代码

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;
            MouseLeftButtonDown += MainWindow_MouseLeftButtonDown;
            MouseRightButtonDown += MainWindow_MouseRightButtonDown;
        }

        private void MainWindow_MouseRightButtonDown(object sender, System.Windows.Input.MouseButtonEventArgs e)
        {
            Point point = e.GetPosition(myPanel);   //获取鼠标点击位置
            Visual visual = GetVisual(point);       //根据点击位置获取命中对象
            if (visual != null)
            {
                myPanel.DeleteVisual(visual);    //删除命中对象
            }
        }

        private void MainWindow_MouseLeftButtonDown(object sender, System.Windows.Input.MouseButtonEventArgs e)
        {
            Point pointClicked=e.GetPosition(myPanel);
            DrawingVisual visual = new DrawingVisual();
            DrawSqure(visual, pointClicked);
            myPanel.AddVisual(visual);
        }

      
        public DrawingVisual GetVisual(Point point) {
            HitTestResult hitTestResult = VisualTreeHelper.HitTest(this, point);
            if (hitTestResult != null)
            {
                return hitTestResult.VisualHit as DrawingVisual;
            }
            else
                return null;
        }
        private void DrawSqure(DrawingVisual visual, Point topLeftCorner)
        {
            DrawingContext dc = visual.RenderOpen();
            Brush brush = Brushes.LightGreen;
            Pen pen = new Pen(Brushes.SteelBlue, 3);
            dc.DrawRectangle(brush, pen,new Rect(topLeftCorner, new Size(50, 50)));
            dc.Close();
            
        }
    }
}

自定义容器类

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);  // 把可视化对象添加到逻辑树上
            base.AddVisualChild(visual);   //把可视化对象添加的可视树上 
        }  
        
        public void DeleteVisual(Visual visual)  //删除可视化元素
        {
            visuals.Remove(visual);
            base.RemoveVisualChild(visual);   
            base.RemoveLogicalChild(visual);
        }

    }
}