gistfile1.m

- (void)viewDidLoad 
{
    [super viewDidLoad];
    [creditCardNumberTextField addTarget:self action:@selector(creditCardNumberFormatter:) forControlEvents:UIControlEventEditingChanged];
    [creditCardExpiryTextField addTarget:self action:@selector(creditCardExpiryFormatter:) forControlEvents:UIControlEventEditingChanged];
}

- (void)creditCardNumberFormatter:(id)sender {
    NSString *formattedText = [StringUtils formatCreditCard:self.creditCardNumberTextField.text]; // this is out formatter
    if (![formattedText isEqualToString:self.creditCardNumberTextField.text]) {
        self.creditCardNumberTextField.text = formattedText;
    }
    if (self.ccNumberTextField.text.length == 19) {
        [self.creditCardNumberTextField resignFirstResponder];
        [self.creditCardExpiryTextField becomeFirstResponder];
    }
}

- (void)creditCardExpiryFormatter:(id)sender {
    NSString *formattedText = [StringUtils formatCreditCardExpiry:self.creditCardExpiryTextField.text];
    if (![formattedText isEqualToString:self.ccExpiryTextField.text]) {
        self.ccExpiryTextField.text = formattedText;
    }
}