In which function do you initiate the execution of animation?

In iOS, animations are usually initiated inside the viewDidAppear(_:) function of a controller, because by this time all interface elements are loaded and displayed on the screen. This allows animations to start correctly when the screen appears. For example:

override func viewDidAppear(_ animated: Bool) {
    super.viewDidAppear(animated)
    UIView.animate(withDuration: 0.5) {
        self.myView.alpha = 1.0
    }
}