Answer by supp-f for What's the best way to validate currency input in UITextField?

I Couldn't find the appropriate implementation for currency validate. Here is my variant:

- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string {

   NSString* proposedString = [textField.text stringByReplacingCharactersInRange:range withString:string];

   //if there is empty string return YES
   if([proposedString length] == 0) {
       return YES;
   }

   //create inverted set for appripriate symbols
   NSCharacterSet *nonNumberSet = [[NSCharacterSet characterSetWithCharactersInString:@"0123456789.,"] invertedSet];

   //if side symbols is trimmed by nonNumberSet - return NO
   if([proposedString stringByTrimmingCharactersInSet:nonNumberSet].length != [proposedString length]) {
       return NO;
   }

   //if there is more than 1 symbol of '.' or ',' return NO
   if([[proposedString componentsSeparatedByCharactersInSet:[NSCharacterSet characterSetWithCharactersInString:@".,"]] count] > 2) {
      return NO;
   }

   //finally check is ok, return YES
   return YES;
}