title: How to disable a button if a text field is empty?
body: <p>I'm trying to disable the continue button if there is nothing in the text field. 
  Here's my code...</p>
  
  <pre><code>import UIKit
  
  class ViewController: UIViewController, UITextFieldDelegate {
  
  @IBOutlet weak var nounTextField: UITextField!
  @IBOutlet weak var `continue`: UIButton!
  
  var noun = String()
  
  override func viewDidLoad() {
      super.viewDidLoad()
  }
  
  @IBAction func continueButton(sender: AnyObject) {
      noun = nounTextField.text!
  }
  override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
      let nvc = segue.destinationViewController as! ViewController2
      nvc.noun2 = noun
  } 
  }
  </code></pre>