如何在XCode Swift 5中通过移动按钮播放简单的淡入淡出动画

我试图在viewDidAppear（）中的xcode中设置按钮的动画：

在ViewWillAspect（）中，首先将按钮的alpha设置为0，然后在ViewDidAspect中按如下方式设置动画：

override func viewDidAppear(_ animated: Bool) {

    UIView.animate(withDuration: 2.0) {
        self.button.alpha = 1
        self.button.frame.origin.y -= 90
        self.button.frame.origin.x -= 10
    }
}
override func viewWillAppear(_ animated: Bool) {

    button.alpha=0
}

override func viewDidAppear(_ animated: Bool) {

    UIView.animate(withDuration: 2.0) {
        self.button.alpha = 1
        self.button.frame.origin.y -= 90
        self.button.frame.origin.x -= 10
    }
}
override func viewWillAppear(_ animated: Bool) {

    button.alpha=0
}