如何使用 MessageBox 确认正确处理 PreviewMouseDown 事件? [英] How do I properly handle a PreviewMouseDown event with a MessageBox confirmation?

问题描述

之前我问过如何取消 WPF TreeViewItem.Selected事件.

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...

<前>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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