ios - 处理失去连接的情况

Question

我使用 Swift 以这种方式从互联网下载数据:

let postEndpoint: String = "http://webisitetest.com"
        guard let url = NSURL(string: postEndpoint) else {
            print("Error: cannot create URL")
            return
        }
        let urlRequest = NSURLRequest(URL: url)

        let config = NSURLSessionConfiguration.defaultSessionConfiguration()
        let session = NSURLSession(configuration: config)

        let task = session.dataTaskWithRequest(urlRequest, completionHandler: { (data: NSData?, response: NSURLResponse?, error: NSError?) in
            // this is where the completion handler code goes
            print(response)
            print(error)
        })

        task.resume()

因为我还下载图像，并且可以在不同的秒数内下载(取决于连接)，如果在下载过程中用户失去连接，我该如何处理这种情况？

我想向他显示一条消息，例如“连接丢失，下载取消，重试”，但我如何捕获此事件？

Answer 1

检查完成处理程序中是否存在错误:

let task = session.dataTaskWithRequest(urlRequest, completionHandler: { (maybeData: NSData?, maybeResponse: NSURLResponse?, maybeError: NSError?) in
    // check for error
    guard maybeError = nil else {
        print(maybeError!)
    }

    // otherwise process the request
    print(maybeResponse)
})