WPF 用户控件命中测试

Question

我有以下用户控件：一个点及其名称：

<UserControl x:Class="ShapeTester.StopPoint"
     xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
     xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
     xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
     xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
     mc:Ignorable="d" 
     d:DesignHeight="25" d:DesignWidth="100">

   <StackPanel>
      <Ellipse Stroke="DarkBlue" Fill="LightBlue" Height="10" Width="10"/>
      <TextBlock Text="Eiffel Tower"/>        
  </StackPanel>
</UserControl>

这很酷。

现在，我有一个面板，我需要恢复我用鼠标点击的 StopPoints：

public partial class StopsPanel : UserControl
{
    private List<StopPoint> hitList = new List<StopPoint>();
    private EllipseGeometry hitArea = new EllipseGeometry();

    public StopsPanel()
    {
        InitializeComponent();
        Initialize();
    }

    private void Initialize()
    {
        foreach (StopPoint point in StopsCanvas.Children)
        {
            point.Background = Brushes.LightBlue;
        }
    }

    private void OnMouseLeftButtonDown(object sender, MouseButtonEventArgs e)
    {
        // Initialization:
        Initialize();
        // Get mouse click point:
        Point pt = e.GetPosition(StopsCanvas);
        // Define hit-testing area:
        hitArea = new EllipseGeometry(pt, 1.0, 1.0);
        hitList.Clear();
        // Call HitTest method:
        VisualTreeHelper.HitTest(StopsCanvas, null,
        new HitTestResultCallback(HitTestCallback),
        new GeometryHitTestParameters(hitArea));
        if (hitList.Count > 0)
        {
            foreach (StopPoint point in hitList)
            {
                // Change rectangle fill color if it is hit:
                point.Background = Brushes.LightCoral;
            }
            MessageBox.Show(string.Format(
                "You hit {0} StopPoint(s)", hitList.Count));
        }
    }

    public HitTestResultBehavior HitTestCallback(HitTestResult result)
    {
        if (result.VisualHit is StopPoint)
        {
            //
            //-------- NEVER ENTER HERE!!! :(
            //

            // Retrieve the results of the hit test.
            IntersectionDetail intersectionDetail =
            ((GeometryHitTestResult)result).IntersectionDetail;
            switch (intersectionDetail)
            {
                case IntersectionDetail.FullyContains:
                // Add the hit test result to the list:
                    hitList.Add((StopPoint)result.VisualHit);
                    return HitTestResultBehavior.Continue;
                case IntersectionDetail.Intersects:
                // Set the behavior to return visuals at all z-order levels:
                    return HitTestResultBehavior.Continue;
                case IntersectionDetail.FullyInside:
                // Set the behavior to return visuals at all z-order levels:
                    return HitTestResultBehavior.Continue;
                default:
                    return HitTestResultBehavior.Stop;
            }
        }
        else
        {
            return HitTestResultBehavior.Continue;
        }
    }
}

因此，如您所见，问题是 HitTest 从未按原样识别 UserControl(StopPoint)，而是它的组件（TextBlock、椭圆甚至边框）。
当我将业务对象关联到 StopPoint 元素时，我需要在 MouseHitting 时获取它，而不是其组合元素。

有办法做到吗？

编辑：

使用过滤器（现在，它根本不进入 HitTestCallback）：

using System.Collections.Generic;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Input;
using System.Windows.Media;

namespace ShapeTester
{
    /// <summary>
    /// Interaction logic for StopsPanel.xaml
    /// </summary>
    public partial class StopsPanel : UserControl
    {
        private List<StopPoint> hitList = new List<StopPoint>();
        private EllipseGeometry hitArea = new EllipseGeometry();

        public StopsPanel()
        {
            InitializeComponent();
            Initialize();
        }

        private void Initialize()
        {
            foreach (StopPoint point in StopsCanvas.Children)
            {
                point.Background = Brushes.LightBlue;
            }
        }

        private void OnMouseLeftButtonDown(object sender, MouseButtonEventArgs e)
        {
            // Initialization:
            Initialize();
            // Get mouse click point:
            Point pt = e.GetPosition(StopsCanvas);
            // Define hit-testing area:
            hitArea = new EllipseGeometry(pt, 1.0, 1.0);
            hitList.Clear();
            // Call HitTest method:
            VisualTreeHelper.HitTest(StopsCanvas, 
                new HitTestFilterCallback(MyHitTestFilter),
                new HitTestResultCallback(HitTestCallback),
                new GeometryHitTestParameters(hitArea));

            if (hitList.Count > 0)
            {
                foreach (StopPoint point in hitList)
                {
                    // Change rectangle fill color if it is hit:
                    point.Background = Brushes.LightCoral;
                }
                MessageBox.Show(string.Format(
                    "You hit {0} StopPoint(s)", hitList.Count));
            }
        }

        public HitTestResultBehavior HitTestCallback(HitTestResult result)
        {
            if (result.VisualHit is StopPoint)
            {
                //
                //-------- NEVER ENTER HERE!!! :(
                //

                // Retrieve the results of the hit test.
                IntersectionDetail intersectionDetail =
                ((GeometryHitTestResult)result).IntersectionDetail;
                switch (intersectionDetail)
                {
                    case IntersectionDetail.FullyContains:
                    // Add the hit test result to the list:
                        hitList.Add((StopPoint)result.VisualHit);
                        return HitTestResultBehavior.Continue;
                    case IntersectionDetail.Intersects:
                    // Set the behavior to return visuals at all z-order levels:
                        return HitTestResultBehavior.Continue;
                    case IntersectionDetail.FullyInside:
                    // Set the behavior to return visuals at all z-order levels:
                        return HitTestResultBehavior.Continue;
                    default:
                        return HitTestResultBehavior.Stop;
                }
            }
            else
            {
                return HitTestResultBehavior.Continue;
            }
        }

        // Filter the hit test values for each object in the enumeration.
        public HitTestFilterBehavior MyHitTestFilter(DependencyObject o)
        {
            // Test for the object value you want to filter.
            if (o.GetType() == typeof(StopPoint))
            {
                // Visual object's descendants are 
                // NOT part of hit test results enumeration.
                return HitTestFilterBehavior.ContinueSkipChildren;
            }
            else
            {
                // Visual object is part of hit test results enumeration.
                return HitTestFilterBehavior.Continue;
            }
        }
    }
}

Answer 1

我想写一个解释，但我已经找到了一个不错的解释：

https://stackoverflow.com/a/7162443/717732

要点是：

您的 UserControl.HitTestCore() 留给了可能返回 NULL 的默认实现，这会导致 UC 被跳过而不是传递给 resultCallback。

默认行为不是错误。这是一个不明显、聪明的设计 - 总而言之，您的控件没有视觉效果，它只是一些具有形状的孩子的容器，因此通常在 UC 中没有必要进行可点击测试并弄乱步行路径。您可能会将其视为一个缺点，因为可命中的 UC 可以使您的代码更加简洁。然而，这里的目标不是简洁，而是速度。事实上，这是一个重要的功能，因为它确实减少了树木漫步者必须执行实际交叉的项目数量！

因此，要么实现 HitTestCore 并返回非空值，要么对 UserControl 的子级进行 hittest，然后当获得正确结果但等于其子级时，使用 VisualTreeHelper.GetParent 直到找到所需的 UserControl。

Answer 2

您可以使用 VisualTreeHelper 来查找父停止点：

var element = result.VisualHit;
while(element != null && !(element is StopPoint))
    element = VisualTreeHelper.GetParent(element);

if(element == null) return;

Answer 3

您是否可以不向这些点添加鼠标单击事件侦听器，而只需将发送者强制转换为 StopPoint 就可以了？不需要额外的命中测试代码。