Detect alphanumeric keystrokes

What’s the nicest way to detect only alphanumeric (international) and symbol keystrokes on a KeyDown-event?

A Simple If - Else - End If block based on the Key’s ASCII value would probably be the most manageable.

If Asc(Key) < 127 And Asc(Key) > 32 Then // It's valid Return False Else // it's invalid Return True // This basically throws the key away End If

Of course, include any special case keys in the test.

Perhaps convert the key to ASCII encoding first. Doing that will convert something like “ü” to “u”.

Thanks Tim & Kem!

The Kem’s advice seems very appropriate to me, just be aware that converting characters that can’t be represented in ASCII you get a “?” (question mark) as the result of conversion.

What could those characters be?


  dim s as string = "€"
  dim a as string = ConvertEncoding(s, encodings.ASCII)

a will contain a question mark.

Right, so do something like this:

dim converted as string = s.ConvertEncoding( Encodings.ASCII )
if converted.Asc >= 32 and ( converted <> "?" or s = "?" ) then
  // Good character
end if

Thanks! Though, I think I need the “Asc(Key) < 127” part to disregard the Del-key.

Oh, right, and 28-31 for the arrow keys, I think, and 13 for the return, 9 for tab, and some other stuff. I’ve done something like this and it took a bit to get it right.