在 VC 上显示 AlertView。当 custom class 在闭包中捕捉到错误

Question

我想问一下关于新的 UIAlertController 的问题。如何检测自定义 class 上的错误以向用户显示警报视图？我想在 switch case 变为默认语句时执行我的警报视图。我的 NetworkOperation class 是自定义的 class，带有用于从网络下载一些 JSON 数据的闭包。

class NetworkOperation {

lazy var config: NSURLSessionConfiguration = NSURLSessionConfiguration.defaultSessionConfiguration()
lazy var session: NSURLSession = NSURLSession(configuration: self.config)

let mainURL: NSURL

typealias JSONWeatherDataDictionary = ([String: AnyObject]?) -> Void

init(url: NSURL) {

    mainURL = url
}

func downloadWeatherDataFromWeb(completion: JSONWeatherDataDictionary) {

    let request = NSURLRequest(URL: mainURL)

    let dataTask = session.dataTaskWithRequest(request) {

        (let data, response, error) in

        if let httpResponse = response as? NSHTTPURLResponse {

            switch httpResponse.statusCode {

            case 200:
                // HTTP Response success use the weather data !

                do {

                    let weatherDataDictionary = try NSJSONSerialization.JSONObjectWithData(data!, options: .MutableContainers) as? [String: AnyObject]

                    completion(weatherDataDictionary)

                } catch {

                    print("Data can't get")
                }

            default:
// I want to execute my alert view in there. showAlertView()
                print("Http Response failed with this code: \(httpResponse.statusCode)")
            }

        } else {

            print("HTTP Response convert fail !")
        }
    }

    dataTask.resume()
}
}

如果执行默认情况，如何在视图控制器中查看我的警报视图？我试图用 UIAlertViewDelegate 解决这个问题，但它已被弃用 iOS9 所以我想学习解决这个问题的最佳常用方法。谢谢大家...

Answer 1

如果您想做的只是显示一个警告让用户知道错误，并提供一个取消按钮以关闭该按钮，您可以使用 UIAlertController.

我用 HTTP URL 测试了以下代码，导致它失败，弹出警报视图显示 status code；并在点击 "cancel" 按钮后自行关闭。

func downloadWeatherDataFromWeb(completion: JSONWeatherDataDictionary)
{
    let request = NSURLRequest(URL: mainURL)
    let dataTask = session.dataTaskWithRequest(request)
    {
        (let data, response, error) in

        if let httpResponse = response as? NSHTTPURLResponse
        {
            switch httpResponse.statusCode
            {
                case 200:
                do
                {
                    let weatherDataDictionary = try NSJSONSerialization.JSONObjectWithData(data!, options: .MutableContainers) as? [String: AnyObject]
                    completion(weatherDataDictionary)
                }
                catch
                {
                    print("Could not retrieve data")
                }
            default:
                print("Http Response failed with the following code: \(httpResponse.statusCode)")

                let alert = UIAlertController(title: "HTTP Error", message:String(httpResponse.statusCode), preferredStyle: UIAlertControllerStyle.Alert)
                //set up cancel action
                let cancelAction: UIAlertAction = UIAlertAction(title: "Cancel", style: .Cancel)
                {
                    action -> Void in
                    //should you want to carry some other operations upon canceling
                }
                //add the action
                alert.addAction(cancelAction)
                dispatch_async(dispatch_get_main_queue(),
                {
                    self.presentViewController(alert, animated:true, completion:
                    {
                        //alert controller presented
                    })
                })
            }
        }
        else
        {
            print("HTTP Response conversion failed!")
        }
    }
    dataTask.resume()
}

更新：回应您的评论

请添加一个UIViewController变量：

class NetworkOperation 
{
    var viewController : UIViewController = UIViewController()
....

并对上面的default:案例进行修改：

dispatch_async(dispatch_get_main_queue(),
{
     self.addChildViewController(self.viewController)
     self.view.addSubview(self.viewController.view)                     
     self.viewController.didMoveToParentViewController(self)
     self.viewController.presentViewController(alert, animated:true,   
     completion:
     {
         //alert controller presented
     })
})

我刚才冒昧地测试了一下；它弹出并关闭。

另一个更新：

然后，我们可以执行以下操作：

dispatch_async(dispatch_get_main_queue(),
{
    let topViewController = UIApplication.sharedApplication().keyWindow?.rootViewController
    topViewController!.presentViewController(alert, animated:true,   
    completion:
    {
     //alert controller presented
    })
})

在 VC 上显示 AlertView。当 custom class 在闭包中捕捉到错误

Show AlertView on VC. When custom class catches the error in closure

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