Using shouldChangeCharactersInRange to limit characters entered, but cannot detect return

Question

I'm using the following code in my UITextField delegate to limit the characters that can be entered:

FYI: The UITextField outlet is called nameChoiceField. Plus there is a label outlet called errorMessageLabel.

- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string 
{
    NSString *potentialNewChosenName = [self.nameChoiceField.text stringByReplacingCharactersInRange:range withString:string];

    NSCharacterSet *nonLettersNumbersOrDashes = [[NSCharacterSet characterSetWithCharactersInString:@"abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890- "] invertedSet];

    if ([potentialNewChosenName stringByTrimmingCharactersInSet:nonLettersNumbersOrDashes].length != potentialNewChosenName.length) {
        self.errorMessageLabel.text = @"Only letters, numbers etc allowed.";
        return NO;
    } else {
        self.errorMessageLabel.text = @"That's okay.";
        return YES;
    }
}

Which works nicely (so long as autocorrect is off, and if you add some other stuff in to stop the auto full stop after you enter 2 spaces).

However! When you tap return on the keyboard, it doesn't allow it (displaying the error message "Only letters....").

How do you restrict the input a user can make, and still have the return button to be recognised?

Also, are there any best practices for recognising the delete button that should be implemented above?

Answer 1

Turns out that:

return is represented by a string of @"\n"

delete is represented by a string of @"" (with the length of the range determining how much gets deleted).