Boilerplate code to validate an email/username UITextField and password UITextField before taking action

UITextFieldDelegate-Validation-Boilerplate.m

- (void)viewDidLoad
{
    [super viewDidLoad];

    self.finishButton.enabled = NO;
    self.emailTextField.delegate = self;
    self.passwordTextField.delegate = self;
}

#pragma mark - UITextFieldDelegate methods

- (void)textFieldDidBeginEditing:(UITextField *)textField {
    
    if (textField == self.emailTextField) {
        if (self.passwordTextField.text.length > 0) {
            [self.finishButton setEnabled:YES];
        }
    } else if (textField == self.passwordTextField) {
        if (self.emailTextField.text.length > 0 && self.passwordTextField.text.length > 0) {
            [self.finishButton setEnabled:YES];
        }
    }
    
}

- (void)textFieldDidEndEditing:(UITextField *)textField {
    if (self.passwordTextField.text.length < 1 || self.emailTextField.text.length < 1) {
        [self.finishButton setEnabled:NO];
    }
    
}

- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string
{
    // enable the arrow if we have enough data
    if (textField == self.emailTextField) {
        if (string.length > 0 && self.passwordTextField.text.length > 0) {
            [self.finishButton setEnabled:YES];
        } else if (string.length == 0 && range.location > 0 && self.passwordTextField.text.length > 0) {
            [self.finishButton setEnabled:YES];
        } else {
            [self.finishButton setEnabled:NO];
        }
    } else if (textField == self.passwordTextField) {
        if (string.length > 0 && self.emailTextField.text.length > 0) {
            [self.finishButton setEnabled:YES];
        } else if (string.length == 0 && range.location > 0 && self.emailTextField.text.length > 0) {
            [self.finishButton setEnabled:YES];
        } else {
            [self.finishButton setEnabled:NO];
        }
    }
    
    return YES;
}

- (BOOL) textFieldShouldReturn:(UITextField *) textField {
	[textField resignFirstResponder];
	if (textField == self.emailTextField) {
        [self.passwordTextField becomeFirstResponder];
    }
	if (textField == self.passwordTextField) {
        [self finishAction:nil];
        [self.emailTextField resignFirstResponder];
    }
    
	return YES;
}


- (IBAction)finishAction:(id)sender {
}