title: UIAlertController Error When called in a modal presented view controller in swift
body: <p>I have a view controller which is modally presented and when i run  UIAlertController, keep getting a error message . how can i work around this.</p>
  
  <p>the alert is trigged from a button which checks a text field is empty or not. </p>
  
  <pre><code>@IBAction func registerAction(sender: AnyObject) {
  if(userEmail.isEmpty){
          alertMessage("Fields Are Empty")
      }
  }
  
  
  
  func alertMessage(userMessage:String){  
      var myAlert = UIAlertController(title: "Alert", message: userMessage, preferredStyle: UIAlertControllerStyle.Alert)
      let okAction = UIAlertAction(title: "OK", style: UIAlertActionStyle.Default, handler: nil)
      myAlert.addAction(okAction)
      self.presentViewController(myAlert, animated: true, completion: nil)
  }
  </code></pre>
  
  <p>Error when i run the alert</p>
  
  <pre><code>Warning: Attempt to present &lt;UIAlertController: 0x7f9bbb9060d0&gt;  on &lt;AlertApp.CustomSignupVC: 0x7f9bb94accb0&gt; which is already presenting &lt;UIAlertController: 0x7f9bbb926660&gt;
  </code></pre>