Text field accept user required characters only

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

    NSString *acceptedCharacters=@""; // only these characters  will be allowed to be displayed in text filed.
    NSCharacterSet *cs = [[NSCharacterSet characterSetWithCharactersInString:acceptedCharacters] invertedSet];

    NSString *filtered = [[string componentsSeparatedByCharactersInSet:cs] componentsJoinedByString:@""];

    return [string isEqualToString:filtered];
}