title: How to blur the viewcontroller when alertcontroller is present?
body: <p>Is it possible to do this ?? I have a UIAlertController which appears in a viewcontroller.What I wish to acheive is to blur/cover the background when the alert is present and once the alert is gone the background should be visible</p>
  
  <p>import UIKit
  import LocalAuthentication
  class TabBarViewController: UITabBarController {</p>
  
  <pre><code>@IBOutlet weak var noteTabBar: UITabBar!
  
  override func viewDidLoad() {
  super.viewDidLoad()
      self.authenticateUser()
      self.tabBar.hidden = false
      self.view.addGestureRecognizer(self.revealViewController().panGestureRecognizer())
  
      let userDefaults = NSUserDefaults.standardUserDefaults()
      userDefaults.setObject(false, forKey: "sendModeToggle")
      userDefaults.setObject("Avenir-Medium", forKey: "font")
       userDefaults.setObject(13, forKey:"fontSize")
              // Do any additional setup after loading the view.
  }
  override func didReceiveMemoryWarning() {
      super.didReceiveMemoryWarning()
      // Dispose of any resources that can be recreated.
  }
  
  
  /*
  // MARK: - Navigation
  
  // In a storyboard-based application, you will often want to do a little preparation before navigation
  override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
      // Get the new view controller using segue.destinationViewController.
      // Pass the selected object to the new view controller.
  }
  */
  
  // MARK: Touch ID Authentication
  
  func authenticateUser()
  {
      let context = LAContext()
      var error: NSError?
      let reasonString = "Authentication is needed to access your app! :)"
  
      let blurEffect = UIBlurEffect(style: .Light)
      let blurVisualEffectView = UIVisualEffectView(effect: blurEffect)
      blurVisualEffectView.frame = view.bounds
  
      if context.canEvaluatePolicy(LAPolicy.DeviceOwnerAuthenticationWithBiometrics, error: &amp;error)
      {
  
          context.evaluatePolicy(LAPolicy.DeviceOwnerAuthenticationWithBiometrics, localizedReason: reasonString, reply: { (success, policyError) -&gt; Void in
  
              if success
              {
                  print("Authentication successful! :) ")
                  blurVisualEffectView.removeFromSuperview()
  
              }
              else
              {
                  switch policyError!.code
                  {
                  case LAError.SystemCancel.rawValue:
                      print("Authentication was cancelled by the system.")
                  /*case LAError.UserCancel.rawValue:
                      print("Authentication was cancelled by the user.")
                   */   
                  case LAError.UserFallback.rawValue:
                      print("User selected to enter password.")
                      NSOperationQueue.mainQueue().addOperationWithBlock({ () -&gt; Void in
                          self.showPasswordAlert()
                      })
                  default:
                      print("Authentication failed! :(")
                      NSOperationQueue.mainQueue().addOperationWithBlock({ () -&gt; Void in
                          self.showPasswordAlert()
                      })
                  }
              }
  
          })
      }
      else
      {
          print(error?.localizedDescription)
          NSOperationQueue.mainQueue().addOperationWithBlock({ () -&gt; Void in
              self.showPasswordAlert()
          })
      }
  
  
  }
  
  // MARK: Password Alert
  
  func showPasswordAlert()
  {
  
      let blurEffect = UIBlurEffect(style: .Light)
      let blurVisualEffectView = UIVisualEffectView(effect: blurEffect)
      blurVisualEffectView.frame = view.bounds
  
  
      let alertController = UIAlertController(title: "Touch ID Password", message: "Please enter your password.", preferredStyle: .Alert)
  
      let defaultAction = UIAlertAction(title: "OK", style: .Cancel) { (action) -&gt; Void in
  
          if let textField = alertController.textFields?.first as UITextField?
          {
              if textField.text == "notes"
              {
                  print("Authentication successful! :) ")
                  blurVisualEffectView.removeFromSuperview()
              }
              else
              {
                  self.showPasswordAlert()
  
              }
          }
      }
      alertController.addAction(defaultAction)
  
      alertController.addTextFieldWithConfigurationHandler { (textField) -&gt; Void in
  
          textField.placeholder = "Password"
          textField.secureTextEntry = true
      }
      self.view.addSubview(blurVisualEffectView)
      self.presentViewController(alertController, animated: true, completion: nil)
  }
  </code></pre>
  
  <p>}</p>