Checking TextCompositionEventArgs.ControlText by Unicode encoding

Question

I'm looking at a WPF example from a book where OnPreviewTextInput is overridden in a class derived from Window. The override checks the TextCompositionEventArgs.ControlText string against the Unicode literal character '\u000F'. This corresponds to the user pressing Ctrl+O.

The character '\u000F' looks like a "magic" literal to me. How would I know what to check for if I wanted to check for other codes? Is there a more reader-friendly way to do this?

protected override void OnPreviewTextInput(TextCompositionEventArgs e)
{
    // Ctrl+O
    if (e.ControlText.Length > 0 && e.ControlText[0] == '\u000F')
    {
        // do stuff
    }
}

Answer 1

As you have surmised, it is a "magic" literal. But there is some logic and history behind the magic. It corresponds to an old concept called Control characters (long read, only if you're interested).

For a quick reference of how 0x0F corresponds to Ctrl-O, see this table. Focus on the first column with the caret notation; you'll see that characters 1-26 (0x01-0x1A) maps Ctrl-A to Ctrl-Z. Char 15 (or 0x0F) is your Ctrl-O.

These old ASCII control codes were brought over to Unicode, retaining their mapping. Hence your '\u0000F'.

If you've been on the internet long enough you'll see some dumb^H^H^H^Hawesome jokes that rely on the arcane knowledge that ^H maps to the Backspace control character. You can actually try some of them. Fire up Notepad, and you'll see that Ctrl-I and Ctrl-M map to Tab and Enter correspondingly.