Question

如果我从服务器得到某个响应，我想只执行一个segue。在swift中，我怎么能等到我得到回复才能继续？

Answer 1

最重要的是，您不要“等待”响应，而是简单地指定响应进入时您想要发生的事情。例如，如果您想在某些网络请求完成时执行segue，应该采用完成处理程序模式。

这里的问题是你可能习惯于在UI Builder中将你的UI控件挂钩到segue。在我们的例子中，我们不想这样做，而是我们想要执行网络请求，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，然后将您的按钮挂钩到执行网络请求的@IBAction，并在适当的情况下以编程方式执行segue。但是，请注意，应该没有直接连接按钮的segue。我们将以编程方式执行此操作。

例如：

通过 control 定义两个视图控制器之间的segue - 从第一个场景上方的条形图中的视图控制器图标拖拽到第二个场景：
通过选择segue并转到“Attributes Inspector”选项卡，为该segue提供一个故事板标识符：
将按钮（或任何将触发此segue的内容）连接到@IBAction。

编写一个执行网络请求的@IBAction，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
}

在swift中，我怎么能等到收到服务器响应才能继续？

1 个答案: