WPF ComboBox Undo Exception on Ctrl+Z (with Focus on SelectionChanged), Why?

Question

Well, someone can tell me why this exception occurs in these conditions?

Test Window

<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>
    <ComboBox
        Name="cmbTest"
        IsEditable="True"
        SelectionChanged="ComboBox_SelectionChanged">
    </ComboBox>
  </StackPanel>
</Window>

Code behind

Class MainWindow

  Sub New()
    ' This call is required by the designer.
    InitializeComponent()

    ' Add any initialization after the InitializeComponent() call.
    Dim source As New ObservableCollection(Of String)()
    source.Add("AAA")
    source.Add("BBB")
    source.Add("CCC")
    cmbTest.ItemsSource = source
  End Sub

  Private Sub ComboBox_SelectionChanged(sender As System.Object, e As System.Windows.Controls.SelectionChangedEventArgs)
    Keyboard.Focus(cmbTest)
  End Sub

End Class

Now, if you type AAA and then Ctrl+Z, ComboBox control raise this exception:

Cannot Undo or Redo while undo unit is open.

Someone can explain why?!? How it would be possible to avoid it?

I have the same problem when moving focus in TextBox.TextChanged. If I put focus back manually (mouse/shiftTab) then Ctrl-Z crashes as well.. :s — EricG, Apr 08 '15 at 13:36
For that particular problem I currently managed to bypass the problem when doin gthe Focus on the UIThread after I invoked it from a Timer.. >.< Just to see if it'd work. Working on more.. — EricG, Apr 08 '15 at 14:53

score 0 · Answer 1 · answered Apr 17 '13 at 14:39

0

"The Undo method does not work with the KeyPress or TextChanged events." This has gotten me before.

Source: http://msdn.microsoft.com/en-us/library/system.windows.forms.textboxbase.undo.aspx

answered Apr 17 '13 at 14:39

MrDosu

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WPF ComboBox Undo Exception on Ctrl+Z (with Focus on SelectionChanged), Why?

1 Answers1