Prevent user from entering Special Characters in a Text input

[WarrenBelz]

This question came from a post I responded to and got me thinking that this was something that may be required at times, so I came up with the model in this blog. It may have other application as well as the Text Box example.

Firstly do a Collection of all special characters (you can do this at Screen OnVisible) by using their ASCII value ranges

ClearCollect(
   colChar,
   ForAll(
      Sequence(15),
      {FieldNo: Char(32 + Value)}
   ),
   ForAll(
      Sequence(7),
      {FieldNo: Char(57 + Value)}
   ),
   ForAll(
      Sequence(5),
      {FieldNo: Char(90 + Value)}
   ),
   ForAll(
      Sequence(4),
      {FieldNo: Char(122 + Value)}
   )
)

this puts 31 Special Characters into the collection under the field FieldNo. There may be some you want to allow such as underscore _ (95) so you would have to adjust the below to suit.
Below is a gallery (with wrap at 4) showing the characters

Now put this on the OnChange of the Text Box

ForAll(
   colChar,
   If(
      FieldNo in Self.Text,
      Collect(
         colError,
         {CharError: true}
      );
      Reset(Self)
   )
)

NOTE - I had to use a Collection here as a Variable cannot be set inside a ForAll() statement.

Put this on the OnSelect of the Text Box - you could also in addition put this at Screen OnVisible 

Clear(colError)

 Now put a Label (this is the warning message) on the screen with this as the Text

"Do not use characters " & Concat(
    colChar,
    FieldNo & ""
) & " here"

and this as the Visible

First(colError).CharError