如何使用 MessageBox 确认正确处理 PreviewMouseDown 事件?

本文介绍了如何使用 MessageBox 确认正确处理 PreviewMouseDown 事件?的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！

问题描述

回答者建议我在选择发生之前处理 PreviewMouseDown 事件.这是有道理的.

我已经尝试这样做了...

XAML...

Visual Basic...

子 TreeViewThings_PreviewMouseDown(...)如果 UnsavedChangesExist() 那么e.Handled = UserCancelled()别的e.处理=假万一结束子函数 UnsavedChangesExist() 作为布尔值...结束函数函数 UserCancelled() 作为布尔值Return MessageBox.Show("放弃你未保存的更改?", _未保存的更改", _MessageBoxButton.OKCancel, _MessageBoxImage.Question) = MessageBoxResult.Cancel结束函数这只是一种工作......
如果没有未保存的更改，那么它会继续执行并执行 TreeViewThings_Selected().
如果有未保存的更改，那么我会看到 MessageBox...
MessageBox:继续并放弃未保存的更改?确定/取消 http://img25.imageshack.us/img25/141/discard2yk0.gif
如果我选择取消，它会取消.
但是，如果我改为选择确定"来放弃我未保存的更改，那么它无论如何都会取消——即使 e.Handled = False.它不会继续执行 TreeViewThings_Selected().
我认为 MessageBox 的存在以某种方式把它搞砸了.
我做错了什么?
 解决方案 
问题是消息框导致您的树失去焦点.您是否尝试在关闭消息框后将焦点设置回树?
Earlier I asked how to cancel a WPF TreeViewItem.Selected event.
The answerers suggested I instead handle the PreviewMouseDown event before the selection even takes place.  That makes sense.
I've tried to do that...
XAML...
<TreeView Name="TreeViewThings"
    ...
    PreviewMouseDown="TreeViewThings_PreviewMouseDown"
    TreeViewItem.Expanded="TreeViewThings_Expanded"
    TreeViewItem.Selected="TreeViewThings_Selected" >
Visual Basic...
Sub TreeViewThings_PreviewMouseDown(...)
    If UnsavedChangesExist() Then
        e.Handled = UserCancelled()
    Else
        e.Handled = False
    End If
End Sub

Function UnsavedChangesExist() As Boolean
    ...
End Function

Function UserCancelled() As Boolean
    Return MessageBox.Show("Discard your unsaved changes?", _
                           "Unsaved Changes", _
                           MessageBoxButton.OKCancel, _
                           MessageBoxImage.Question) = MessageBoxResult.Cancel
End Function
This is only sort of working...
If there are no unsaved changes, then it proceeds just fine and executes TreeViewThings_Selected().
If there are unsaved changes, then I see the MessageBox...
MessageBox: Continue and discard your unsaved changes?  OK/Cancel http://img25.imageshack.us/img25/141/discard2yk0.gif
If I then choose Cancel, it cancels.
However, If I instead choose OK to discard my unsaved changes, then it just cancels anyway--even though e.Handled = False.  It does not continue on and execute TreeViewThings_Selected().
I think the fact that there's a MessageBox screws it up somehow.
What am I doing wrong?
 解决方案 
The problem is that the messagebox causes your tree to lose focus.  Have you tried setting the focus back to the tree after the messagebox is dismissed?
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handled

如何使用 MessageBox 确认正确处理 PreviewMouseDown 事件?

问题描述