防止事件冒泡:WPF&Rx

我有一个小的WPF应用程序,它在画布上绘制一些点,然后跟踪鼠标在任何点内移动后的移动,直到鼠标在画布上移动。我的问题是如何防止点里面的鼠标垫冒泡到画布上。我想让画布鼠标下坠的观察者在鼠标下坠时开火 外部 圆点,当且仅当圆点内部发生鼠标下坠时,圆点下坠观察者才会开火。

下面是我构建可观察链的技巧,显示如果DownInAndTrackWrtObservable的第三个参数为true,则在触发mouseDown事件中设置EventArgs.Handled属性:

private IObservable<BasedVector> DownInAndTrackWrtObservable(
    UIElement hitTestElement, 
    UIElement trackWrtElement,
    bool handleItP = false)
{
    var hitObs = hitTestElement.GetLeftMouseDownObservable();

    var trackObs = from mDown in hitObs
                   let mDownP = mDown.EventArgs.GetPosition(hitTestElement)
                   from mMove in trackWrtElement.GetMouseMoveObservable().
                       TakeUntil(trackWrtElement.GetLeftMouseUpObservable())
                   select new {D = mDown, P = mDownP, M = mMove};

    if (handleItP)
        trackObs.Subscribe(e =>
            e.D.EventArgs.Handled = true);

    return from obs in trackObs 
           select new BasedVector
           (
               tail: obs.P,
               head: obs.M.EventArgs.GetPosition(trackWrtElement)
           );
}

然后,我在两个地方设置了处理程序,一个是跟踪画布上的点击、点和拖动

DownInAndTrackWrtObservable(ellipse, canvas1, handleItP:true).Subscribe(bv =>
{
    PointMouseDownTextBox.Text =
        String.Format("Point {2} MouseDown({0:G}, {1:G})", bv.Tail.X, bv.Tail.Y, ellipse.Uid);
    CanvasMouseMoveTextBox.Text =
        String.Format("Canvas MouseMove({0:G}, {1:G})", bv.Head.X, bv.Head.Y);
});

和

DownInAndTrackWrtObservable(canvas1, canvas1).Subscribe(bv =>
{
    CanvasMouseDownTextBox.Text =
        String.Format("Canvas MouseDown({0:G}, {1:G})", bv.Tail.X, bv.Tail.Y);
    CanvasMouseMoveTextBox.Text =
        String.Format("Canvas MouseMove({0:G}, {1:G})", bv.Head.X, bv.Head.Y);
});

问题是,当鼠标下移发生在点上时,画布上的鼠标下移仍然会被检测到,如第二个处理程序所示。但我不希望因为设置了Event.Handled属性而发生这种情况。顺便说一句,如果我设置了事件。在hitObs而不是trackObs上处理,那么在点内根本检测不到命中。 这是完整的应用程序,带有它的XAML(请“添加引用”到System.coreex、System.Reactive和System.Interactive)

using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Input;
using System.Windows.Shapes;

namespace WpfTest
{
    public static partial class UIElementExtensions
    {
        public static IObservable<IEvent<MouseButtonEventArgs>>
            GetLeftMouseDownObservable(this UIElement uiElement)
        {
            return Observable.FromEvent<MouseButtonEventHandler, MouseButtonEventArgs>(
               h => new MouseButtonEventHandler(h),
               h => uiElement.MouseLeftButtonDown += h,
               h => uiElement.MouseLeftButtonDown -= h);
        }

        public static IObservable<IEvent<MouseButtonEventArgs>>
            GetLeftMouseUpObservable(this UIElement uiElement)
        {
            return Observable.FromEvent<MouseButtonEventHandler, MouseButtonEventArgs>(
               h => new MouseButtonEventHandler(h),
               h => uiElement.MouseLeftButtonUp += h,
               h => uiElement.MouseLeftButtonUp -= h);
        }

        public static IObservable<IEvent<MouseEventArgs>>
            GetMouseMoveObservable(this UIElement uiElement)
        {
            return Observable.FromEvent<MouseEventHandler, MouseEventArgs>(
               h => new MouseEventHandler(h),
               h => uiElement.MouseMove += h,
               h => uiElement.MouseMove -= h);
        }
    }

    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
            Draw();
        }

        private static double scaleCanvasPerWorld = 150D;
        private static Point offsetInCanvas = new Point(15D, 15D);
        private static Point worldOrigin = new Point();
        private static Point WorldToCanvas(Point worldPoint)
        {
            // Difference of two points gives a System.Drawing.Vector, which has operator overloads.
            var result = ((worldPoint - worldOrigin) * scaleCanvasPerWorld + offsetInCanvas);
            return result;
        }
        private static Point CanvasToWorld(Point canvasPoint)
        {
            var result = ((canvasPoint - offsetInCanvas) / scaleCanvasPerWorld);
            return (Point)result;
        }

        private void DrawPoint(Point worldPoint)
        {
            var ellipse = new Ellipse();
            ellipse.Stroke = System.Windows.Media.Brushes.Black;
            ellipse.Fill = System.Windows.Media.Brushes.Black;
            ellipse.HorizontalAlignment = HorizontalAlignment.Center;
            ellipse.VerticalAlignment = VerticalAlignment.Center;
            ellipse.Width = 12;
            ellipse.Height = 12;

            var canvasPoint = WorldToCanvas(worldPoint);
            ellipse.SetValue(Canvas.LeftProperty, canvasPoint.X);
            ellipse.SetValue(Canvas.TopProperty, canvasPoint.Y);

            DownInAndTrackWrtObservable(ellipse, canvas1, handleItP: true).Subscribe(bv =>
            {
                PointMouseDownTextBox.Text =
                    String.Format("Point {2} MouseDown({0:G}, {1:G})", bv.Tail.X, bv.Tail.Y, ellipse.Uid);
                CanvasMouseMoveTextBox.Text =
                    String.Format("Canvas MouseMove({0:G}, {1:G})", bv.Head.X, bv.Head.Y);
            });

            canvas1.Children.Add(ellipse);
        }

        private class BasedVector
        {
            public Point Tail { get; set; }
            public Point Head { get; set; }
            public Vector Vector { get; set; }
            public BasedVector(Point tail, Point head)
            {
                Debug.Assert(tail != null);
                Debug.Assert(head != null);

                this.Tail = tail;
                this.Head = head;

                this.Vector = head - tail;
            }
        }

        private IObservable<BasedVector> DownInAndTrackWrtObservable(
            UIElement hitTestElement,
            UIElement trackWrtElement,
            bool handleItP = false)
        {
            var hitObs = hitTestElement.GetLeftMouseDownObservable();

            var trackObs = from mDown in hitObs
                           let mDownP = mDown.EventArgs.GetPosition(hitTestElement)
                           from mMove in trackWrtElement.GetMouseMoveObservable().
                               TakeUntil(trackWrtElement.GetLeftMouseUpObservable())
                           select new { D = mDown, P = mDownP, M = mMove };

            if (handleItP)
                trackObs.Subscribe(e =>
                    e.D.EventArgs.Handled = true);

            return from obs in trackObs
                   select new BasedVector
                   (
                       tail: obs.P,
                       head: obs.M.EventArgs.GetPosition(trackWrtElement)
                   );
        }

        private void Draw()
        {
            var controlPoints = new Point[]
            {
                new Point(0D, 0D),
                new Point(0D, 1D),
                new Point(0.5D, 1D),
                new Point(1.5D, 0D),
                new Point(2D, 0D),
                new Point(2D, 1D),
            };

            controlPoints.Run(DrawPoint);

            DownInAndTrackWrtObservable(canvas1, canvas1).Subscribe(bv =>
            {
                CanvasMouseDownTextBox.Text =
                    String.Format("Canvas MouseDown({0:G}, {1:G})", bv.Tail.X, bv.Tail.Y);
                CanvasMouseMoveTextBox.Text =
                    String.Format("Canvas MouseMove({0:G}, {1:G})", bv.Head.X, bv.Head.Y);
            });
        }
    }
}

以及XAML

<Window x:Class="WpfTest.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="MainWindow" mc:Ignorable="d" xmlns:d="http://schemas.microsoft.com/expression/blend/2008" xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" Height="350" Width="522">
    <Grid Height="313" Name="grid1" Width="500" >
        <Canvas Height="237" HorizontalAlignment="Left" Margin="0,75,0,0" Name="canvas1" VerticalAlignment="Top" Width="500" Background="#00000000" />
        <StackPanel Height="52" HorizontalAlignment="Left" Margin="12,12,0,0" Name="stackPanel1" VerticalAlignment="Top" Width="200">
            <TextBox Height="23" Name="CanvasMouseDownTextBox" Width="186" BorderBrush="Blue" />
            <TextBox Height="23" Name="PointMouseDownTextBox" Width="186" BorderBrush="Blue" />
        </StackPanel>
        <StackPanel Height="52" HorizontalAlignment="Left" Margin="211,12,0,0" Name="stackPanel2" VerticalAlignment="Top" Width="200">
            <TextBox Height="23" Name="CanvasMouseMoveTextBox" Width="186" BorderBrush="Blue" />
        </StackPanel>
    </Grid>
</Window>

会很感激你的建议