In your login IBAction, send the LoginViewController the pushViewController: animated:
message. That message and its counter-part, popViewControllerAnimated:
is available in the UINavigationController class.
Unfortunately, your LoginViewController isn't a UINavigationController.
You can fix that particular error by changing it to:
[self.navigationController pushViewController:self.dataController animated:YES];
That assumes that LoginViewController is being hosted by a UINavigationController.