当任务太短时，加载覆盖会导致问题答案

【问题标题】：Loading overlay causes issues when task is too short当任务太短时，加载覆盖会导致问题
【发布时间】：2018-07-12 12:41:10
【问题描述】：

我正在根据这个主题使用加载模式：

Loading an "overlay" when running long tasks in iOS

我在几个 ViewController 中使用相同的代码，所以我创建了一个扩展：

extension UIViewController {
    func showLoading() {
        let alert = UIAlertController(title: nil, message: "Please wait...", preferredStyle: .alert)

        let loadingIndicator = UIActivityIndicatorView(frame: CGRect(x: 10, y: 5, width: 50, height: 50))
        loadingIndicator.hidesWhenStopped = true
        loadingIndicator.activityIndicatorViewStyle = UIActivityIndicatorViewStyle.gray
        loadingIndicator.startAnimating();

        alert.view.addSubview(loadingIndicator)

        present(alert, animated: false, completion: nil)
    }

    func hideLoading() {
        if ( presentedViewController != nil && !presentedViewController!.isBeingPresented ) {
            dismiss(animated: false, completion: nil)
        }
    }
}

我通常使用这样的代码：

self.showLoading()
callNetwork() { response in
    DispatchQueue.main.async {
       self.hideLoading()
       ....
    }
}

如果网络调用需要 0.5 秒或更长时间，则一切正常。问题是网络是否太快。然后我会得到一个类似的错误：

Warning: Attempt to dismiss from view controller <UINavigationController: 0x7ff581830a00> while a presentation or dismiss is in progress!

而且模态不会被关闭。

我能想到的最好的解决方案是这样的（超类而不是扩展，因为扩展不能有变量）：

class LoadingViewController: UIViewController {
    var shouldDismissImmediately = false

    func showLoading() {
        shouldDismissImmediately = false
        let alert = UIAlertController(title: nil, message: "Please wait...", preferredStyle: .alert)

        let loadingIndicator = UIActivityIndicatorView(frame: CGRect(x: 10, y: 5, width: 50, height: 50))
        loadingIndicator.hidesWhenStopped = true
        loadingIndicator.activityIndicatorViewStyle = UIActivityIndicatorViewStyle.gray
        loadingIndicator.startAnimating();

        alert.view.addSubview(loadingIndicator)

        present(alert, animated: false) {
             if (self.shouldDismissImmediately) {
                 self.dismiss(animated: false, completion: nil)
             }
        }
    }

    func hideLoading() {
        if ( presentedViewController != nil && !presentedViewController!.isBeingPresented ) {
            dismiss(animated: false, completion: nil)
        } else {
           shouldDismissImmediately = true
        }
    }
}

谁能想到更好的解决方案？就是这个感觉不太对。也许我在做一些根本错误的事情。就像 - 在等待网络响应时，我什至应该呈现这样的对话框吗？有没有更好的方法让用户等待？我需要用户意识到正在发生某些事情，同时我需要他不能按 UI 中的任何按钮。

【问题讨论】：

标签： ios iphone swift

【解决方案1】：

extension UIViewController {
    func showLoading(finished: @escaping () -> Void) {
        let alert = UIAlertController(title: nil, message: "Please wait...", preferredStyle: .alert)

        let loadingIndicator = UIActivityIndicatorView(frame: CGRect(x: 10, y: 5, width: 50, height: 50))
        loadingIndicator.hidesWhenStopped = true
        loadingIndicator.activityIndicatorViewStyle = UIActivityIndicatorViewStyle.gray
        loadingIndicator.startAnimating();

        alert.view.addSubview(loadingIndicator)

        present(alert, animated: false, completion: finished)
    }

    func hideLoading(finished: @escaping () -> Void) {
        if ( presentedViewController != nil && !presentedViewController!.isBeingPresented ) {
            dismiss(animated: false, completion: finished)
        }
    }
}

self.showLoading(finished: {
    callNetwork() {
        DispatchQueue.main.async {
            self.hideLoading(finished: {
                // done
             })
         }
     }
})

【讨论】：