当应用程序从Firebase实时数据库接收数据时,如何显示UIActivityIndicator

您需要在firebase observer回调范围外开始设置UIActivityIndicatorView的动画,并在观察者返回快照后停止。

var activityIndicator: UIActivityIndicatorView! 

override func viewDidLoad() {
  var activityIndicator = UIActivityIndicatorView(activityIndicatorStyle: 
   UIActivityIndicatorViewStyle.Gray) 
   activityIndicator.hidesWhenStopped = true; 
   activityIndicator.isHidden = true 
   activityIndicator.center = view.center;
   addSubview(myActivityIndicator)
   super.viewDidLoad()
}

func firebaseObserver() {
  // Show indicator 
  activityIndicator.isHidden = false
  activityIndicator.startAnimating()

  // Firebase network observer 
  let connectedRef = Database.database().reference(withPath: ".info/connected")
connectedRef.observe(.value, with: { snapshot in

   // Stop and hide indicator
   self.activityIndicator.stopAnimating()
   self.activityIndicator.isHidden = true

   // Proceed with other operations.
     })
}