title: use of undeclared type UIViewController
body: <p>I have not changed anything major in this swift file, yet for some reason when I went to run my app I got a new error stating "Use of undeclared type UIViewController" in the first line of my swift file.  I have tried cleaning and checking the targets, but am unable to figure out the issue.</p>
  
  <p>I am getting an errors on every line below, excluding the import statements</p>
  
  <pre><code>import Foundation
  import FirebaseAuth
  import FirebaseDatabase    
  
  public class User: UIViewController {
          @IBOutlet weak var _Fname: UITextField!
          @IBOutlet weak var _Lname: UITextField!
          @IBOutlet weak var _Email: UITextField!
          @IBOutlet weak var _Password1: UITextField!
          @IBOutlet weak var _Password2: UITextField!
  </code></pre>
  
  <p>Please let me know if you have any thoughts on why this may be occurring.  Thanks in advance!</p>