WPF ComboBox with IsEditable=“True” - How can I indicate that no match was found?

Question

Using the following simple text box as an example:

    Angus/ComboBoxItem         


        

Answer 1

This solution is based on user1234567's answer, with a couple changes. Instead of searching the Items list it simply checks the ComboBox's SelectedIndex for a value >= 0 to see if a match was found and it resolves RB's concern about holding down a key inserting more than one character. It also adds an audible feedback when it rejects characters.

private int _lastMatchLength = 0;

private void myComboBox_GotFocus(object sender, RoutedEventArgs e)
{
    _lastMatchLength = 0;
}

private void myComboBox_KeyUp(object sender, KeyEventArgs e)
{
    ComboBox cBox = sender as ComboBox;

    TextBox tb = cBox.Template.FindName("PART_EditableTextBox", cBox) as TextBox;
    if (tb != null)
    {
        if (cBox.SelectedIndex >= 0)
        {
            _lastMatchLength = tb.SelectionStart;
        }
        else if (tb.Text.Length == 0)
        {
            _lastMatchLength = 0;
        }
        else
        {
            System.Media.SystemSounds.Beep.Play();
            tb.Text = tb.Text.Substring(0, _lastMatchLength);
            tb.CaretIndex = tb.Text.Length;
        }
    }
}