swift - 迅速，我如何才能等到收到服务器响应后再继续？

Question

如果我从服务器得到某个响应，我只想执行一个 segue。迅速，我怎么能等到我得到回复才能继续？

Answer 1

最重要的是，您不会“等待”响应，而是简单地指定响应到来时您希望发生的事情。例如，如果您想在完成某些网络请求时执行 segue，您应该使用完成处理程序模式。

这里的问题是您可能习惯于将您的 UI 控件与 Interface Builder 中的 segue 挂钩。在我们的例子中，我们不想这样做，而是想要执行网络请求，然后让它的完成处理程序以编程方式调用 segue。因此，我们必须创建一个可以以编程方式执行的 segue，然后将您的按钮连接到@IBAction执行网络请求的按钮上，如果合适的话，以编程方式执行 segue。但是，请注意，不应该直接连接到按钮的 segue。我们将以编程方式进行。

例如：

1. control通过从第一个场景上方栏中的视图控制器图标拖动到第二个场景，将 segue 定义为两个视图控制器之间：

   

2. 通过选择 segue 并转到“Attributes Inspector”选项卡，为该 segue 提供故事板标识符：

   

3. 将按钮（或任何会触发此 segue 的东西）连接到@IBAction.

   

4. 编写一个@IBAction执行网络请求，并在完成后以编程方式调用该 segue：

   @IBAction func didTapButton(_ sender: Any) {
       let request = URLRequest(...).       // prepare request however your app requires
   
       let waitingView = showWaitingView()  // present something so that the user knows some network request is in progress
   
       // perform network request
   
       let task = URLSession.shared.dataTask(with: request) { data, response, error in
           // regardless of how we exit this, now that request is done, let's 
           // make sure to remove visual indication that network request was underway
   
           defer {
               DispatchQueue.main.async {
                   waitingView.removeFromSuperview()
               }
           }
   
           // make sure there wasn't an error; you'll undoubtedly have additional
           // criteria to apply here, but this is a start
   
           guard let data = data, error == nil else {
               print(error ?? "Unknown error")
               return
           }
   
           // parse and process the response however is appropriate in your case, e.g., if JSON:
           //
           // guard let responseObject = try? JSONSerialization.jsonObject(with data) else {
           //     // handle parsing error here
           //     return
           // }
           //
           // // do whatever you want with the parsed JSON here
   
           // do something with response
   
           DispatchQueue.main.async {
               performSegue(withIdentifier: "SegueToSceneTwo", sender: self)
           }
       }
       task.resume()
   }
   
   /// Show some view so user knows network request is underway
   ///
   /// You can do whatever you want here, but I'll blur the view and add `UIActivityIndicatorView`.
   
   private func showWaitingView() -> UIView {
       let effectView = UIVisualEffectView(effect: UIBlurEffect(style: .Dark))
       effectView.translatesAutoresizingMaskIntoConstraints = false
       view.addSubview(effectView)
       NSLayoutConstraint.activateConstraints([
           effectView.leadingAnchor.constraintEqualToAnchor(view.leadingAnchor),
           effectView.trailingAnchor.constraintEqualToAnchor(view.trailingAnchor),
           effectView.topAnchor.constraintEqualToAnchor(view.topAnchor),
           effectView.bottomAnchor.constraintEqualToAnchor(view.bottomAnchor)
       ])
   
       let spinner = UIActivityIndicatorView(activityIndicatorStyle: .WhiteLarge)
       effectView.addSubview(spinner)
       spinner.translatesAutoresizingMaskIntoConstraints = false
       NSLayoutConstraint.activateConstraints([
           spinner.centerXAnchor.constraintEqualToAnchor(view.centerXAnchor),
           spinner.centerYAnchor.constraintEqualToAnchor(view.centerYAnchor)
       ])
       spinner.startAnimating()
   
       return effectView
   }