WPF 已知问题 Popup 吃掉 PreviewMouseDown 事件
在 WPF 中,使用 Popup 也许会看到 PreviewMouseDown 事件被吃掉
因为 PreviewMouseDown 是 RoutingStrategy.Direct 路由事件,不能在多个视觉树使用,在设置 Popup 点击界面 StaysOpen="False" 的逻辑就在下面代码
private void OnPreviewMouseButton(MouseButtonEventArgs e)
{
// We should only react to mouse buttons if we are in an auto close mode (where we have capture)
if (_cacheValid[(int)CacheBits.CaptureEngaged] && !StaysOpen)
{
Debug.Assert( Mouse.Captured == _popupRoot.Value, "_cacheValid[(int)CacheBits.CaptureEngaged] == true but Mouse.Captured != _popupRoot");
// If we got a mouse press/release and the mouse isn't on the popup (popup root), dismiss.
// When captured to subtree, source will be the captured element for events outside the popup.
if (_popupRoot.Value != null && e.OriginalSource == _popupRoot.Value)
{
// When we have capture we will get all mouse button up/down messages.
// We should close if the press was outside. The MouseButtonEventArgs don't tell whether we get this
// message because we have capture or if it was legit, so we have to do a hit test.
if (_popupRoot.Value.InputHitTest(e.GetPosition(_popupRoot.Value)) == null)
{
// The hit test didn't find any element; that means the click happened outside the popup.
SetCurrentValueInternal(IsOpenProperty, BooleanBoxes.FalseBox);
}
}
}
}
如果写一个 CheckBox 放在界面上,运行代码可以看到可以被打勾但是没有事件
<Grid>
<StackPanel>
<Button Margin="10,10,10,10" Content="Open Popup" Click="OpenPopup_OnClick"></Button>
<CheckBox PreviewMouseDown="UIElement_OnPreviewMouseDown"></CheckBox>
</StackPanel>
<Popup x:Name="Popup" StaysOpen="False">
<Grid Width="100" Height="100" Background="White">
<TextBlock HorizontalAlignment="Center" VerticalAlignment="Center" Text="Popup"></TextBlock>
</Grid>
</Popup>
</Grid>
在 UIElement_OnPreviewMouseDown
添加输出内容,代码如下,可以看到,没有符合预期输出
private void UIElement_OnPreviewMouseDown(object sender, MouseButtonEventArgs e)
{
Debug.WriteLine("PreviewMouseDown");
}
private void OpenPopup_OnClick(object sender, RoutedEventArgs e)
{
Popup.PlacementTarget = (UIElement) sender;
Popup.Placement = PlacementMode.Mouse;
Popup.IsOpen = true;
}
本文代码放在 github 欢迎访问
此问题已报告 WPF 官方,请看 Known issus: Popup with “StaysOpen=false” steals PreviewMouseDown event · Issue #2166 · dotnet/wpf
更多请看 dotnet 读 WPF 源代码 Popup 的 StaysOpen 为 false 将会吃掉其他窗口的首次激活
博客园博客只做备份,博客发布就不再更新,如果想看最新博客,请访问 https://blog.lindexi.com/
如图片看不见,请在浏览器开启不安全http内容兼容
![知识共享许可协议](https://licensebuttons.net/l/by-nc-sa/4.0/88x31.png)
本作品采用知识共享署名-非商业性使用-相同方式共享 4.0 国际许可协议进行许可。欢迎转载、使用、重新发布,但务必保留文章署名[林德熙](https://www.cnblogs.com/lindexi)(包含链接:https://www.cnblogs.com/lindexi ),不得用于商业目的,基于本文修改后的作品务必以相同的许可发布。如有任何疑问,请与我[联系](mailto:lindexi_gd@163.com)。