关于 swift:UIActivityIndi??catorView 未显示在 iOS UIViewController 中

UIActivityIndicatorView not showing up in iOS UIViewController

我想在视图中心的视图控制器中显示一个灰色的 UIViewIndicatorView，但是这段代码没有显示任何内容：

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20

class MyViewController: UIViewController {
var activityIndicatorView = UIActivityIndicatorView()

override func viewDidLoad() {
super.viewDidLoad()
view.backgroundColor = .black
displayActivityIndicator()
}

func displayActivityIndicator() {
view.addSubview(activityIndicatorView)
activityIndicatorView.style = .gray
activityIndicatorView.translatesAutoresizingMaskIntoConstraints = false
activityIndicatorView.centerXAnchor.constraint(equalTo: view.centerXAnchor).isActive = true
activityIndicatorView.widthAnchor.constraint(equalToConstant: 40).isActive = true
activityIndicatorView.heightAnchor.constraint(equalToConstant: 40).isActive = true
activityIndicatorView.centerYAnchor.constraint(equalTo: view.centerYAnchor).isActive = true
activityIndicatorView.startAnimating()
}
}

仅当我将视图控制器的视图设置为类似白色(不包括黑色)的颜色时，才会显示活动指示器视图。

我怎样才能让它显示出来？

改变背景为

1	view.backgroundColor = .green // for example

或

1	activityIndicatorView.style = .white

然后你会看到它，因为它几乎是指示器和背景视图之间的颜色匹配