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单击菜单会导致表单“失去焦点”，并且菜单下拉菜单消失

[英]Menu click causes form to “lose focus” and menu dropdown disappears

原文 2014-02-18 17:08:56 2 3 c#/ contextmenustrip/ menustrip

I have noticed some strange form interactions while using a ContextMenuStrip or a MenuStrip . 我注意到在使用ContextMenuStrip或MenuStrip时发生了一些奇怪的表单交互。 I don't really know what is causing it so the following should create a repeatable test for anyone looking into this: 我真的不知道是什么原因造成的，因此以下内容应该为任何关注此问题的人创建可重复的测试：

I've created two Windows Forms: Form1 and Form2 . 我创建了两个Windows窗体： Form1和Form2 。 Both have a MenuStrip added to them. 两者都添加了MenuStrip 。 Both are set to StartPosition = CenterScreen . 两者都设置为StartPosition = CenterScreen 。

Form1 has a simple menu like this: Form2 > Open . Form1具有一个简单的菜单，如下所示： Form2 > Open 。 Clicking "Open" will launch Form2 . 单击“打开”将启动Form2 。

Form2 has a simple menu like this: Try to open > anotherTestMenuItem Form2具有一个简单的菜单，如下所示： Try to open > anotherTestMenuItem

Start the program. 启动程序。 Form1 opens. Form1打开。
Open Form2 from Form1 (ie click Form2 > Open ). 从Form1打开Form2 （即，单击Form2 > Open ）。
Form2 appears. Form2出现。
On Form2 , try to open the MenuStrip (click Try to open ). 在Form2 ，尝试打开MenuStrip （单击“ Try to open ）。 Form1 will reappear over Form2 , although Form2 still has focus (you can see this if you move Form2 a little before trying to open the menu). Form1将重新出现在Form2 ，虽然Form2仍然具有焦点（你可以看到这一点，如果你移动Form2试图打开菜单有点过了）。

If I set Form2 's owner to Form1 , Form2 remains visible when you try Step 4, but the menu doesn't display the first time. 如果我将Form2的所有者设置为Form1 ，则在尝试执行步骤4时， Form2仍然可见，但是菜单不会第一次显示。 All subsequent clicks seem fine. 以后所有的点击似乎都很好。

I noticed this when I tried opening a context menu (on a form opened by another form) and it would disappear immediately, but only the first time. 当我尝试打开一个上下文菜单（在另一个表单打开的表单上）时，我注意到了这一点，它会立即消失，但这只是第一次。 Every time thereafter it would open normally. 此后每次它将正常打开。

Does anyone have any ideas as to what is going on? 有人对发生的事情有任何想法吗？

3 个解决方案

Yes, this is a known bug in the RTM version of .NET 4.5. 是的，这是.NET 4.5的RTM版本中的一个已知错误。 This KB article mentions it: 此知识库文章提到了它：

When you click a menu item to open a child window in the application, interactions with the menu and child windows behave incorrectly. 当您单击菜单项以在应用程序中打开子窗口时，与菜单和子窗口的交互行为不正确。

For example, you may experience the following: 例如，您可能会遇到以下情况：
- When you open a shortcut menu in the child window, the main window form takes the focus. -在子窗口中打开快捷菜单时，主窗口窗体将成为焦点。
- You cannot use mnemonics to access a menu item. -您不能使用助记符访问菜单项。

As you can tell from the KB article, this bug was fixed quite a while ago. 正如您从知识库文章中看到的那样，此错误已在很早之前修复。 The bug fix was incorporated in a maintenance release first made available on January 8th of 2013. Be sure to allow Windows Update to deploy that update on your machine. 该错误修复程序包含在2013年1月8日首次发布的维护版本中。请确保允许Windows Update在您的计算机上部署该更新。 Or download it from here . 或从这里下载。

Check to see that you have: 检查您是否拥有：

"AutoValidate" set to "EnablePreventFocusChange" 将“自动验证”设置为“ EnablePreventFocusChange”

Make sure you do not call the Hide method for a menu or contextmenu during its item-click handler. 确保在菜单项或上下文菜单的项目单击处理程序中未调用其Hide方法。 I was in the habit of doing this during development to get a menu off the screen while I stepped through debugging code. 我习惯于在开发过程中执行此操作，以便在逐步调试代码时从屏幕上获得菜单。 However when I launched a secondary form from such a menu, the first right-click in the new form would cause the focus to revert to the primary form, sometimes even if I had left-clicked or typed something in the new form. 但是，当我从这样的菜单启动辅助表单时，即使在新表单中左键单击或键入某些内容时，第一次在新表单中单击鼠标右键也会使焦点恢复为主要表单。 I don't recall if I found this solution online somewhere or discovered it myself. 我不记得我是在某个地方在线找到该解决方案还是自己发现了它。 This may not be the same bug mentioned above, but this behavior still occurs in .NET 4.7. 这可能与上面提到的错误不同，但是在.NET 4.7中仍然会发生此行为。