WPF ComboBox, force input to UpperCase

I have an editable WPF ComboBox with TextSearchEnabled. I need to force the user's text input to uppercase when they type to filter the ComboBox.

I was thinking of modifying the textbox that is part of the control (named 'PART_EditableTextBox') to set CharacterCasing="Upper", however I can't quite figure out how to do this.

Do I need to use a trigger, or modify the templat开发者_开发知识库e in some way?

This works and seems like a reasonable solution:

protected void winSurveyScreen_Loaded(object sender, RoutedEventArgs e)
{
    (comboBox.Template.FindName("PART_EditableTextBox", cbObservation) as TextBox).CharacterCasing = CharacterCasing.Upper;
}

Ensure that the combobox is not collapsed on loaded otherwise the template will not be found.

IMO, the quicker way is to set the UpdateTrigger to PropertyChanged and, in the data object, uppercase the value when it is updated.

I found that post where the attached property is used. That permit to use that for all of your ComboBox without rewriting the code.

private void TextBox_PreviewTextInput(object sender, TextCompositionEventArgs e)
{
    Textbox editableTextbox = sender as Textbox;
    foreach (char ch in e.Text)
    {
        if (Char.IsLower(ch))
        {
            editableTextbox.Text += Char.ToUpper(ch);
            e.Handled = true;
        }
    }
}

or try creating an attached behaviour for the textbox