Detect alphanumeric keystrokes

General
1

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

2

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.

3

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

4

Thanks Tim & Kem!

5

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.

6

What could those characters be?

7

Example:

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

a will contain a question mark.

8

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
9

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

10

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.