URLSession.datatask 请求块未在后台调用

Question

URLSession 数据任务块在应用程序处于后台时未调用，它因请求而卡在 dataTask。
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()

当应用程序处于活动状态时完美运行。我的代码有什么问题吗？请点我

Answer 1

您需要后台会话。 Apple 文档中的 URLSessionDataTask 不支持后台下载。

创建一个 URLSessionDownloadTask 并使用它应该工作的委托方法。

关注这个link

Answer 2

  [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];

//如图应用

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

Answer 3

如果您希望在您的应用程序不再处于前台后继续下载，您必须使用后台会话。 Downloading Files in Background 中概述了后台会话的基本限制，本质上是：

使用基于委托的 URLSession 背景 URLSessionConfiguration。
仅使用上传和下载任务，没有完成处理程序。
在 iOS 中，实施 application(_:handleEventsForBackgroundURLSession:completionHandler:) 应用委托，保存完成处理程序并启动后台会话。

在您的 URLSessionDelegate 中实施 urlSessionDidFinishEvents(forBackgroundURLSession:)，调用已保存的完成处理程序让 OS 知道您已完成后台请求完成处理。

所以，把它们放在一起：

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)
}

在哪里

class BackgroundSession: NSObject {
    static let shared = BackgroundSession()
    
    static let identifier = "com.domain.app.bg"
    
    private var session: URLSession!

    #if !os(macOS)
    var savedCompletionHandler: (() -> Void)?
    #endif
    
    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 {
    #if !os(macOS)
    func urlSessionDidFinishEvents(forBackgroundURLSession session: URLSession) {
        DispatchQueue.main.async {
            self.savedCompletionHandler?()
            self.savedCompletionHandler = nil
        }
    }
    #endif
}

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)")
        }
    }
}

并且 iOS 应用程序委托执行：

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

Answer 4

或者干脆开始 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)
  }
}

URLSession.datatask 请求块未在后台调用

URLSession.datatask with request block not called in background

xcode

ios

nsurlsession

swift

xcode8