WPF ComboBox, force input to UpperCase

Question

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

Answer 1

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