c# - 即使光标在 Canvas 之外，也会调用 MouseMove 事件。 `Border` Canvas 周围没有工作

Question

future 情况的简短描述:

只要鼠标移到我的 Canvas 上，我就想在 Canvas 上显示一个椭圆。在用户点击鼠标左键之前，椭圆应该会一直跟随鼠标移动。当用户点击鼠标左键时，程序应将椭圆放置在 Canvas 上。

因此我使用了以下 xaml 代码:

    <Window x:Class="WpfApplication1.MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="MainWindow" Height="700" Width="1200">



<Grid>
    <Border ClipToBounds="true">
    <Canvas x:Name="canvasss" Background="AntiqueWhite" Width="524" Height="368" MouseMove="Canvasss_MouseMove" MouseDown="Canvasss_MouseDown">

    </Canvas>
    </Border>
</Grid>

C# 代码:

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

    namespace WpfApplication1
    {
         public class Item
         {
            private readonly Ellipse shape;

            public Item(Canvas canvas)
            {
                shape = new Ellipse { Width = 50, Height = 50, Fill = Brushes.Black };
                canvas.Children.Add(shape);
                SetPosition(0.0, 0.0);
            }

            public void SetPosition(double x, double y)
            {
                Canvas.SetLeft(shape, x);
                Canvas.SetTop(shape, y);
            }
        }

        public partial class MainWindow : Window
        {
            private readonly IList<Item> shapes;
            private Item currentMovingShape;

            public MainWindow()
            {
                InitializeComponent();
                shapes = new List<Item>();
                InitMovingShape();
            }

            private void InitMovingShape()
            {
                currentMovingShape = new Item(canvasss);
            }

            private void SetMovingShapePosition(MouseEventArgs e)
            {
                var pos = e.GetPosition(canvasss);
                currentMovingShape.SetPosition(pos.X - 25, pos.Y - 25);
            }

            private void Canvasss_MouseMove(object sender, MouseEventArgs e)
            {
                var pos = e.GetPosition(canvasss);
                currentMovingShape.SetPosition(pos.X - 25, pos.Y - 25);
            }

            private void Canvasss_MouseDown(object sender, MouseButtonEventArgs e)
            {
                shapes.Add(currentMovingShape);
                InitMovingShape();            
            }


         }
    }

问题是，一旦鼠标离开 Canvas ，椭圆仍然粘在鼠标上，甚至可以将椭圆放在 Canvas 之外。

首先，我使用代码(代码来自 stijn:C# - WPF - Mousemove event on canvas will overload the mouse events so click event is not fired)，在 xaml 代码中 Canvas 周围没有 Border。然后我读到它可能有助于在 Canvas 周围放置一个 Border ( MouseMove event is called even when cursor is outside of canvas ) 并将其实现到 xaml 代码中，如您所见。不幸的是，它没有帮助。

有人可以帮我解决吗？代码解决方案将不胜感激，因为我是 c# 的初学者。

Answer 1

看起来你想实现 Adorners在你的控制之下。请务必阅读它们，因为它们会派上用场，以便在 wpf 中轻松执行此类操作。

但是，要解决您的问题。您应该在代码中实现 MouseEnter 和 MouseLeave 事件。在 MouseEnter 上添加形状，在 MouseLeave 或 MouseDown 上移除形状。因此，当鼠标重新进入 Canvas 时，MouseEnter 逻辑将启动并添加形状，而您的 MouseMove 逻辑将使用鼠标移动形状。希望我在这里说清楚。如果您仍在为代码苦苦挣扎，请告诉我。

编辑

xaml

<Grid Background="Transparent">
        <Canvas x:Name="canvasss" Background="AntiqueWhite" Width="300" Height="300"  MouseEnter="canvasss_MouseEnter" MouseLeave="canvasss_MouseLeave"  MouseMove="Canvasss_MouseMove" MouseDown="Canvasss_MouseDown" Margin="50" HorizontalAlignment="Center" VerticalAlignment="Center"/>
    </Grid>

代码

public partial class MainWindow : Window
    {
        private readonly IList<Ellipse> shapes;
        private Ellipse currentMovingShape;
        public MainWindow()
        {
            InitializeComponent();
            shapes = new List<Ellipse>();
        }

        private void canvasss_MouseEnter(object sender, MouseEventArgs e)
        {
            AddEllipse();
        }

        private void AddEllipse()
        {
            currentMovingShape = new Ellipse { Width = 50, Height = 50, Fill = Brushes.Black };
            currentMovingShape.IsHitTestVisible = false;
            canvasss.Children.Add(currentMovingShape);
            Canvas.SetLeft(currentMovingShape, Mouse.GetPosition(canvasss).X - 25);
            Canvas.SetTop(currentMovingShape, Mouse.GetPosition(canvasss).Y - 25);
        }

        private void canvasss_MouseLeave(object sender, MouseEventArgs e)
        {
            if (currentMovingShape != null)
            {
                canvasss.Children.Remove(currentMovingShape);
                currentMovingShape = null;
            }
        }
        private void Canvasss_MouseMove(object sender, MouseEventArgs e)
        {
            Canvas.SetLeft(currentMovingShape, e.GetPosition(canvasss).X - 25);
            Canvas.SetTop(currentMovingShape, e.GetPosition(canvasss).Y - 25);
        }

        private void Canvasss_MouseDown(object sender, MouseButtonEventArgs e)
        {
            if (currentMovingShape != null)
            {
                currentMovingShape.IsHitTestVisible = true;
                shapes.Add(currentMovingShape);
                AddEllipse();
            }

        }
    }