Question

当应用程序处于后台时，

URLSession数据任务块未调用，并且dataTask请求处于停留状态。
当我打开应用程序时，块被调用。顺便说一句，我正在使用https请求这是我的代码：

    let request = NSMutableURLRequest(url: URL(string: url as String)!,

                                      cachePolicy: .reloadIgnoringCacheData,

                                      timeoutInterval:20)

    request.httpMethod = method as String

    request.setValue("application/x-www-form-urlencoded", forHTTPHeaderField: "Content-Type")

    let session = URLSession.shared

    let data = params.data(using: String.Encoding.utf8.rawValue)

    request.httpBody = data

    session.dataTask(with: request as URLRequest,completionHandler:

        {(data, response, error) -> Void in

         if error == nil

            {

                do {

                    let result = try JSONSerialization.jsonObject(with: data!, options:

                        JSONSerialization.ReadingOptions.mutableContainers)

                    print(result)

                     completionHandler(result as AnyObject?,nil)

                }

                catch let JSONError as NSError{

                    completionHandler(nil,JSONError.localizedDescription as NSString?)

                }

            }

            else{

                completionHandler(nil,error!.localizedDescription as NSString?)                    

            }                

    }).resume()

当应用处于活动状态时，可以正常工作。我的代码有什么问题。请指点我

Answer 1

如果您希望在应用不再位于前台后进行下载，则必须使用后台会话。背景会话的基本限制在URL Session Programming Guide: Using NSURLSession: Background Transfer Considerations中列出，基本上是：

使用基于代理的URLSession与背景URLSessionConfiguration。
仅使用上传和下载任务，没有完成处理程序。
在您的app委托中实施application(_:handleEventsForBackgroundURLSession:completionHandler:)，保存完成处理程序并启动后台会话。

在URLSessionDelegate中实施urlSessionDidFinishEvents(forBackgroundURLSession:)，调用已保存的完成处理程序，让操作系统知道您已完成处理后台请求的完成。

所以，把它拉到一起：

func startRequest(for urlString: String, method: String, parameters: String) {
    let url = URL(string: urlString)!
    var request = URLRequest(url: url, cachePolicy: .reloadIgnoringCacheData, timeoutInterval: 20)
    request.httpMethod = method
    request.setValue("application/x-www-form-urlencoded", forHTTPHeaderField: "Content-Type")
    request.httpBody = parameters.data(using: .utf8)
    BackgroundSession.shared.start(request)
}

其中

class BackgroundSession: NSObject {
    static let shared = BackgroundSession()

    static let identifier = "com.domain.app.bg"

    private var session: URLSession!

    var savedCompletionHandler: (() -> Void)?

    private override init() {
        super.init()

        let configuration = URLSessionConfiguration.background(withIdentifier: BackgroundSession.identifier)
        session = URLSession(configuration: configuration, delegate: self, delegateQueue: nil)
    }

    func start(_ request: URLRequest) {
        session.downloadTask(with: request).resume()
    }
}

extension BackgroundSession: URLSessionDelegate {
    func urlSessionDidFinishEvents(forBackgroundURLSession session: URLSession) {
        DispatchQueue.main.async {
            self.savedCompletionHandler?()
            self.savedCompletionHandler = nil
        }
    }
}

extension BackgroundSession: URLSessionTaskDelegate {
    func urlSession(_ session: URLSession, task: URLSessionTask, didCompleteWithError error: Error?) {
        if let error = error {
            // handle failure here
            print("\(error.localizedDescription)")
        }
    }
}

extension BackgroundSession: URLSessionDownloadDelegate {
    func urlSession(_ session: URLSession, downloadTask: URLSessionDownloadTask, didFinishDownloadingTo location: URL) {
        do {
            let data = try Data(contentsOf: location)
            let json = try JSONSerialization.jsonObject(with: data)

            print("\(json)")
            // do something with json
        } catch {
            print("\(error.localizedDescription)")
        }
    }
}

应用代表确实：

func application(_ application: UIApplication, handleEventsForBackgroundURLSession identifier: String, completionHandler: @escaping () -> Void) {
    BackgroundSession.shared.savedCompletionHandler = completionHandler
}

Answer 2

您需要一个后台会话。根据Apple的文档，URLSessionDataTask不支持后台下载。

创建一个URLSessionDownloadTask并使用它应该有效的委托方法。

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Answer 3

或者直接启动BackgroundTask

func send(...) {
  let backgroundTaskID = UIApplication.shared.beginBackgroundTask(expirationHandler: nil)
  let session = URLSession(configuration: .default)

  // ... after all the main logic, when you finish:
  DispatchQueue.main.async {
    completion(result)
    UIApplication.shared.endBackgroundTask(backgroundTaskID)
  }
}

Answer 4

  [URLSessionDownloadTask setDownloadTaskDidWriteDataBlock:^(NSURLSession *session, NSURLSessionDownloadTask *downloadTask, int64_t bytesWritten, int64_t totalBytesWritten, int64_t totalBytesExpectedToWrite) {
                CGFloat percentDone = (double)(totalBytesWritten)/(double)totalBytesExpectedToWrite;
                [SVProgressHUD showWithStatus:[NSString stringWithFormat:@"%.2f%%",percentDone*100]];

            }];

        [downloadTask resume];

//如图所示申请

/ ********************* /

URLSession.datatask，后台没有调用请求块

4 个答案: