鼠标离开时关闭Popup弹窗：DragDrop捕获致常规方法失效

因为DragDrop.DoDragDrop()会触发系统级鼠标捕获，直接导致WPF的MouseEnter/Leave事件、IsMouseOver属性完全失效，所以得换思路检测鼠标是否离开Popup范围：

方法一：通过全局DragOver事件实时检测 #

在拖拽启动时注册全局DragOver事件，每次拖拽移动时检查鼠标是否在Popup的屏幕范围内，一旦超出就关闭Popup并终止拖拽：

XAML代码 #

<Popup x:Name="targetPopup" StaysOpen="False">
    <Border Width="200" Height="200" Background="#FFF">
        <Rectangle x:Name="draggableElement" Width="60" Height="60" Fill="#00F"
                   PreviewMouseLeftButtonDown="DraggableElement_PreviewMouseLeftButtonDown"/>
    </Border>
</Popup>

C#后台代码 #

private void DraggableElement_PreviewMouseLeftButtonDown(object sender, MouseButtonEventArgs e)
{
    // 注册全局拖拽移动事件
    Application.Current.DragOver += OnGlobalDragOver;
    try
    {
        // 启动拖拽
        DragDrop.DoDragDrop(draggableElement, "拖拽数据", DragDropEffects.Copy);
    }
    finally
    {
        // 拖拽结束后清理事件绑定
        Application.Current.DragOver -= OnGlobalDragOver;
    }
}

private void OnGlobalDragOver(object sender, DragEventArgs e)
{
    // 计算Popup在屏幕上的矩形范围
    var popupScreenTopLeft = targetPopup.PointToScreen(new Point(0, 0));
    var popupScreenRect = new Rect(popupScreenTopLeft, 
                                   new Size(targetPopup.ActualWidth, targetPopup.ActualHeight));
    
    // 获取当前鼠标的屏幕位置
    var mouseScreenPos = Mouse.GetPosition(null);
    
    // 判断鼠标是否超出Popup范围
    if (!popupScreenRect.Contains(mouseScreenPos))
    {
        targetPopup.IsOpen = false;
        // 终止拖拽操作
        e.Effects = DragDropEffects.None;
        e.Handled = true;
    }
}

方法二：用DispatcherTimer定时轮询检测 #

如果全局DragOver事件触发不灵敏，可以启动一个定时器，每隔几十毫秒检查一次鼠标位置：

C#后台代码 #

private DispatcherTimer _dragMonitorTimer;

private void DraggableElement_PreviewMouseLeftButtonDown(object sender, MouseButtonEventArgs e)
{
    _dragMonitorTimer = new DispatcherTimer { Interval = TimeSpan.FromMilliseconds(50) };
    _dragMonitorTimer.Tick += OnDragMonitorTick;
    _dragMonitorTimer.Start();

    try
    {
        DragDrop.DoDragDrop(draggableElement, "拖拽数据", DragDropEffects.Copy);
    }
    finally
    {
        _dragMonitorTimer.Stop();
        _dragMonitorTimer = null;
    }
}

private void OnDragMonitorTick(object sender, EventArgs e)
{
    var popupScreenTopLeft = targetPopup.PointToScreen(new Point(0, 0));
    var popupScreenRect = new Rect(popupScreenTopLeft, 
                                   new Size(targetPopup.ActualWidth, targetPopup.ActualHeight));
    var mouseScreenPos = Mouse.GetPosition(null);

    if (!popupScreenRect.Contains(mouseScreenPos))
    {
        targetPopup.IsOpen = false;
        _dragMonitorTimer.Stop();
        // 强制终止拖拽
        DragDrop.DoDragDrop(draggableElement, null, DragDropEffects.None);
    }
}

关键说明 #

• 两种方法核心都是计算Popup的屏幕坐标范围，再对比鼠标的屏幕位置，避开系统鼠标捕获对WPF元素事件的影响。
• 拖拽结束后一定要清理事件或定时器，避免内存泄漏。

内容的提问来源于stack exchange，提问作者user13251051