Private _isTabStop As Boolean

Private Sub MainWindow_Initialized(sender As Object, e As EventArgs)
　　KeyboardNavigation.SetTabNavigation(Me.TestComboBox, KeyboardNavigationMode.None)
　　AddHandler Me.KeyDown, AddressOf form_KeyDown
　　_isTabStop = Me.TestComboBox.IsTabStop
End Sub

Private Sub form_KeyDown(sender As Object, e As KeyEventArgs)
　　If e.Key = Key.Tab Then
　　　　Me.TestComboBox.IsTabStop = _isTabStop
　　End If
End Sub

Private Sub TabStop_Click(sender As Object, e As RoutedEventArgs)
　　If Me.TestComboBox.IsTabStop = True Then
　　　　Me.TestComboBox.IsTabStop = False
　　　　_isTabStop = False
　　Else
　　　　Me.TestComboBox.IsTabStop = True
　　　　_isTabStop = True
　　End If
End Sub

private bool _isTabStop;

private void Window_Initialized(object sender, EventArgs e)
{
　　KeyboardNavigation.SetTabNavigation(this.TestComboBox, KeyboardNavigationMode.None);
　　this.KeyDown += new KeyEventHandler(form_KeyDown);
　　_isTabStop = this.TestComboBox.IsTabStop;
}

private void form_KeyDown(object sender, KeyEventArgs e)
{
　　if (e.Key == Key.Tab)
　　　 this.TestComboBox.IsTabStop = _isTabStop;
}

private void TabStop_Click(object sender, RoutedEventArgs e)
{
　　if (this.TestComboBox.IsTabStop)
　　{
　　　　this.TestComboBox.IsTabStop = false;
　　　　_isTabStop = false;
　　}
　　else
　　{
　　　　this.TestComboBox.IsTabStop = true;
　　　　_isTabStop = true;
　　}
}