How to check if all characters in a string are valid

Problem/Question/Abstract:

Is there a simple way of checking if all characters in a string are valid? For example valid chars are: "ABCabcd123". If the string I want to check contains "AA23c" it is valid, if it contains "AAY" it is invalid.

Answer:

This is one way to do it:

{ ... }
const
  ValidChars = 'ABCabcd123';
type
  EInvalidText = class(Exception);
var
  iCount: Integer;
begin
  for iCount := 1 to Length(Edit1.Text) do
    if Pos(Edit1.Text[iCount], ValidChars) = 0 then
      raise EInvalidText.Create('Invalid text entered.');
end;