Assigning a value for view asynchronously

UIImageView *imgView = //alloc, get it from a nib, whatever;
[imgView setImageWithURL:[NSURL URLWithString:@"StringPath"]];

 {   
 ImageViewcontroller *imageView=[[ImagesViewController alloc]initwithnibname:@"ImageViewController" bundle:nil];       
 }

override func viewDidLoad() {
    super.viewDidLoad()

    self.view.backgroundColor = UIColor.blue
    let sceneView = UIView(frame: self.view.frame)
    sceneView.backgroundColor = UIColor.red
    self.view.addSubview(sceneView)
}

override func viewDidLoad() {
    super.viewDidLoad()

    self.view.backgroundColor = UIColor.blue
    let sceneView = UIView(frame: self.view.frame)
    sceneView.backgroundColor = UIColor.red
    self.view = sceneView
}

override func loadView() {
    let sceneView = UIView(frame: UIScreen.main.bounds)
    sceneView.backgroundColor = UIColor.red
    self.view = sceneView
}

function function_A(assistant) {
    let key_a = assistant.getArgument(KEY_A_NAME); 
    retrieve_from_database(database_a, key_a, PROPERTY_A_NAME).then(function(property) {
      if (property == null) {
        assistant.tell('Error Message');
      }
      else {
        <do something with property>
      }
    }
}