WPF中MouseDown与MouseUp事件绑定问题：跨对象创建连接失效

你说得完全没错，这就是WPF鼠标捕获机制导致的：当你在某个元素上触发MouseDown时，该元素会自动“抓住”鼠标，后续所有的鼠标事件（包括MouseUp）都会发送给这个捕获了鼠标的元素，哪怕你此时已经把鼠标移到了另一个元素上方。

下面给你几种实用的解决思路，都是我实际开发中用过的方案：

方法1：绑定全局MouseUp事件到父容器 #

最稳妥的方式是把MouseUp事件绑定到父容器（比如你的myCanvas），这样不管鼠标在哪个子元素上松开，都能触发事件，再通过InputHitTest找到松开时命中的对象：

private MyThumb inherObj1;
private Line connector;

private void myThumb1_MouseDown(object sender, MouseButtonEventArgs e)
{
    inherObj1 = sender as MyThumb;
    // 创建初始连接线
    connector = new Line 
    { 
        X1 = e.GetPosition(myCanvas).X, 
        Y1 = e.GetPosition(myCanvas).Y, 
        X2 = e.GetPosition(myCanvas).X, 
        Y2 = e.GetPosition(myCanvas).Y, 
        Stroke = Brushes.Black 
    };
    myCanvas.Children.Add(connector);
    
    // 手动捕获鼠标，确保拖拽时能跟踪位置
    inherObj1.CaptureMouse();
    // 绑定鼠标移动事件来更新连接线
    myCanvas.MouseMove += MyCanvas_MouseMove;
    // 绑定全局MouseUp到画布
    myCanvas.MouseUp += MyCanvas_MouseUp;
}

private void MyCanvas_MouseMove(object sender, MouseEventArgs e)
{
    if (connector != null)
    {
        // 实时更新连接线的终点位置
        connector.X2 = e.GetPosition(myCanvas).X;
        connector.Y2 = e.GetPosition(myCanvas).Y;
    }
}

private void MyCanvas_MouseUp(object sender, MouseButtonEventArgs e)
{
    // 先释放鼠标捕获
    inherObj1?.ReleaseMouseCapture();
    
    // 检测鼠标松开时命中的元素
    var targetThumb = myCanvas.InputHitTest(e.GetPosition(myCanvas)) as MyThumb;
    if (targetThumb != null && inherObj1 != null && targetThumb != inherObj1)
    {
        // 创建两个对象的连接
        CreateInher(inherObj1, targetThumb);
    }
    
    // 清理资源和事件绑定
    myCanvas.MouseMove -= MyCanvas_MouseMove;
    myCanvas.MouseUp -= MyCanvas_MouseUp;
    inherObj1 = null;
    connector = null;
}

这个方案的优势是逻辑清晰，不需要处理复杂的捕获转移，适合大多数场景。

方法2：用WPF内置的拖拽框架（DragDrop） #

如果你的场景是典型的“拖拽连接”，WPF自带的DragDrop框架会更省心，它已经封装了鼠标捕获、拖拽反馈等逻辑：

private void myThumb_MouseDown(object sender, MouseButtonEventArgs e)
{
    var sourceThumb = sender as MyThumb;
    // 启动拖拽，传递源对象数据
    DragDrop.DoDragDrop(sourceThumb, sourceThumb, DragDropEffects.Link);
}

private void myThumb_DragEnter(object sender, DragEventArgs e)
{
    // 只接受MyThumb类型的拖拽数据
    e.Effects = e.Data.GetDataPresent(typeof(MyThumb)) 
        ? DragDropEffects.Link 
        : DragDropEffects.None;
}

private void myThumb_Drop(object sender, DragEventArgs e)
{
    if (e.Data.GetDataPresent(typeof(MyThumb)))
    {
        var inherObj1 = e.Data.GetData(typeof(MyThumb)) as MyThumb;
        var inherObj2 = sender as MyThumb;
        
        if (inherObj1 != null && inherObj2 != null && inherObj1 != inherObj2)
        {
            CreateInher(inherObj1, inherObj2);
        }
    }
}

记得要给所有的MyThumb都绑定DragEnter和Drop事件。这个方案的好处是代码更简洁，还能轻松自定义拖拽时的视觉效果。

方法3：手动转移鼠标捕获 #

如果你一定要在MyThumb的MouseUp事件里处理，可以在鼠标移动到第二个MyThumb上时，把鼠标捕获转移过去：

private MyThumb inherObj1;
private Line connector;

private void myThumb_MouseDown(object sender, MouseButtonEventArgs e)
{
    inherObj1 = sender as MyThumb;
    connector = new Line 
    { 
        X1 = e.GetPosition(myCanvas).X, 
        Y1 = e.GetPosition(myCanvas).Y, 
        X2 = e.GetPosition(myCanvas).X, 
        Y2 = e.GetPosition(myCanvas).Y, 
        Stroke = Brushes.Black 
    };
    myCanvas.Children.Add(connector);
    
    inherObj1.CaptureMouse();
    // 给所有MyThumb绑定MouseEnter事件，用于转移捕获
    foreach (var thumb in myCanvas.Children.OfType<MyThumb>())
    {
        thumb.MouseEnter += Thumb_MouseEnter;
    }
}

private void Thumb_MouseEnter(object sender, MouseEventArgs e)
{
    if (inherObj1 != null && sender is MyThumb targetThumb && targetThumb != inherObj1)
    {
        // 释放原捕获，转移到当前hover的thumb
        inherObj1.ReleaseMouseCapture();
        targetThumb.CaptureMouse();
    }
}

private void myThumb_MouseUp(object sender, MouseButtonEventArgs e)
{
    var targetThumb = sender as MyThumb;
    if (inherObj1 != null && targetThumb != null && targetThumb != inherObj1)
    {
        CreateInher(inherObj1, targetThumb);
    }
    
    // 清理事件和捕获
    foreach (var thumb in myCanvas.Children.OfType<MyThumb>())
    {
        thumb.MouseEnter -= Thumb_MouseEnter;
    }
    targetThumb?.ReleaseMouseCapture();
    inherObj1 = null;
    connector = null;
}

这个方案需要注意遍历所有MyThumb来绑定/解绑事件，避免内存泄漏。

内容的提问来源于stack exchange，提问作者D. Malakhov