title: How to present an alert after view controller has been dismissed
body: <p>I have an app where a user uploads a file in the background that usually takes a couple of seconds.  The upload is kicked off when they tap a "Done" button and that also dismisses the view controller.  What I would I would like to happen is an alert comes up when the download is done.  I thought I would just add the code below to the upload function but it isn't working. How can I have an alert box appear to confirm that that the upload was successful?</p>
  
  <pre><code>@IBAction func tapDone(_ sender: Any) {
      self.dismiss(animated: true, completion: nil)
      if let image = newImage {
          submit2Parse(image: image)
      }
  }
  
  func submit2Parse (image: UIImage) {
      if let pfImage = image2PFFile(image: image) {
          // Insert PFFile into parse server
          let submittedImage = PFObject(className: "Images")
          submittedImage["imageFile"] = pfImage
          submittedImage["type"] = "submittedFromUserHome"
          submittedImage["bride"] = brideSwitch.isOn
          submittedImage["groom"] = groomSwitch.isOn
          submittedImage["user"] = userSwitch.isOn
          submittedImage["picturePeriod"] = pickerSelected
          submittedImage["uploadedByUserId"] = PFUser.current()?.objectId ?? ""            submittedImage["uploadedByUserName"] = PFUser.current()?.username ?? ""
          if !txtIsPlaceHolder { submittedImage["description"] = imageDescription.text }
  
          submittedImage.saveInBackground { (success, error) in
              if success {
                  let message = "Save in bg worked"
                  print(message)
                  let alert = UIAlertController(title: title, message: message, preferredStyle: UIAlertController.Style.alert)
                  alert.addAction(UIAlertAction(title: "Ok", style: UIAlertAction.Style.default, handler: {
                      (action) in
                      self.dismiss(animated: true, completion: nil)
                  }))
                  self.present(alert,animated: true, completion: nil)
  
              } else {
                  print(error?.localizedDescription ?? "")
              }
          }
      }
  }
  </code></pre>
  
  <p>The code gives me this build error:</p>
  
  <blockquote>
    <p>Implicit use of 'self' in closure; use 'self.' to make capture semantics explicit</p>
  </blockquote>