WPF拖放 - 何时DragLeave火？ [英] WPF Drag Drop - When Does DragLeave Fire?

问题描述

我是从父拖动到子控件的时候得到DragLeave事件。我只希望当一个控制的范围之外移动获得此事件。我怎样才能实现呢？

I am getting DragLeave Events when dragging from a parent to child control. I would only expect to get this event when moving outside the bounds of a control. How can I implement this?

请参考这个简单的示例应用程序。

Please refer to this simple sample application.

<Window x:Class="MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="MainWindow" Height="350" Width="525">
    <StackPanel>
        <TextBox Height="50" >Hilight and Drag this text</TextBox>
        <Border BorderBrush="Blue" BorderThickness="2">
            <StackPanel AllowDrop="True" Name="Stack" >
                <Label >If I drag text across the gray line, Stack.DragLeave will fire.</Label>
                <Separator></Separator>
                <Label>I only expect to get this event when leaving the blue rectangle. </Label>
            </StackPanel>
        </Border>
        <TextBlock >Stack.DragLeave Count: <Label x:Name="countLabel" /></TextBlock>
    </StackPanel>
</Window>

和后面

Class MainWindow

    Private Sub Stack_DragLeave(ByVal sender As Object, ByVal e As System.Windows.DragEventArgs) Handles Stack.PreviewDragLeave
        countLabel.Content = countLabel.Content + 1
    End Sub

End Class

推荐答案

我最近一直在正在使用WPF拖/放广泛我自己的应用程序，并花了半天后（调试，谷歌搜索，重新阅读文档）在完全同样的问题，你所看到的，我只能断定有一个未来增强在WPF库中的某个地方埋了。

I've recently been working on my own application that is using WPF drag/drop extensively and after spending half a day (debugging, googling, re-reading documentation) on exactly same issue you are seeing, I could only conclude there's a "future enhancement" buried somewhere in WPF library.

这是我的解决办法：

    protected virtual void OnTargetDragLeave(object sender, DragEventArgs e)
    {
        _dragInProgress = false;

        // It appears there's a quirk in the drag/drop system.  While the user is dragging the object
        // over our control it appears the system will send us (quite frequently) DragLeave followed 
        // immediately by DragEnter events.  So when we get DragLeave, we can't be sure that the 
        // drag/drop operation was actually terminated.  Therefore, instead of doing cleanup
        // immediately, we schedule the cleanup to execute later and if during that time we receive
        // another DragEnter or DragOver event, then we don't do the cleanup.
        _target.Dispatcher.BeginInvoke( new Action( ()=> {
                                if( _dragInProgress == false ) OnRealTargetDragLeave( sender, e ); } ) );
    }

    protected virtual void OnTargetDragOver(object sender, DragEventArgs e)
    {
        _dragInProgress = true;

        OnQueryDragDataValid( sender, e );
    }

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