ios - urlSession :dataTask:didReceive:completionHandler not called in Xcode8 Swift3

Question

我创建了一个背景URLSession使用以下代码的对象:

let identifier = /* some background identifier */
let config = URLSessionConfiguration.background(withIdentifier: identifier)
self.session = URLSession(configuration: config, delegate: self, delegateQueue: nil)

我还实现了以下 URLSessionDataDelegate委托(delegate)类中的方法:

public func urlSession(_ session: URLSession, dataTask: URLSessionDataTask, didReceive response: URLResponse, completionHandler: @escaping (URLSession.ResponseDisposition) -> Void) {
    // code goes here
}

public func urlSession(_ session: URLSession, dataTask: URLSessionDataTask, didReceive data: Data) {
    // code goes here
}

public func urlSession(_ session: URLSession, task: URLSessionTask, didCompleteWithError error: Error?) { 
    // code goes here
}

我可以成功调用 URLSessionUploadTask从本次 session 使用以下内容:

let fileURl = /* some file url */
let request = /* some URLRequest */
let task = session.uploadTask(with: request, fromFile: fileUrl)
task.resume()

但由于某种原因，我只收到以下回调:

`urlSession(_ session: URLSession, task: URLSessionTask, didCompleteWithError error: Error?)` 

和

`urlSession(_ session: URLSession, dataTask: URLSessionDataTask, didReceive data: Data)`.

委托(delegate)方法:

`urlSession(_ session: URLSession, dataTask: URLSessionDataTask, didReceive response: URLResponse, completionHandler: @escaping (URLSession.ResponseDisposition) -> Void)`

永远不会被调用。

这是 Xcode8 中的错误还是我错过了一些重要的东西？
谢谢您的帮助!

Answer 1

Apple SDK 直接引用此方法:

/*
 * Messages related to the operation of a task that delivers data
 * directly to the delegate.
 */
@protocol NSURLSessionDataDelegate <NSURLSessionTaskDelegate>
@optional
/* The task has received a response and no further messages will be
 * received until the completion block is called. The disposition
 * allows you to cancel a request or to turn a data task into a
 * download task. This delegate message is optional - if you do not
 * implement it, you can get the response as a property of the task.
 *
 * This method will not be called for background upload tasks (which cannot be converted to download tasks).
 */
- (void)URLSession:(NSURLSession *)session dataTask:(NSURLSessionDataTask *)dataTask
                                 didReceiveResponse:(NSURLResponse *)response
                                  completionHandler:(void (^)(NSURLSessionResponseDisposition disposition))completionHandler;

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