第25月25日 urlsession

1.

private lazy var session: URLSession = {
    let configuration = URLSessionConfiguration.default
    configuration.waitsForConnectivity = true
    return URLSession(configuration: configuration,
                      delegate: self, delegateQueue: nil)
}()

Listing 3 

Using a delegate with a URL session data task

var receivedData: Data?

func startLoad() {
    loadButton.isEnabled = false
    let url = URL(string: "https://www.example.com/")!
    receivedData = Data()
    let task = session.dataTask(with: url)
    task.resume()
}

// delegate methods

func urlSession(_ session: URLSession, dataTask: URLSessionDataTask, didReceive response: URLResponse,
                completionHandler: @escaping (URLSession.ResponseDisposition) -> Void) {
    guard let response = response as? HTTPURLResponse,
        (200...299).contains(response.statusCode),
        let mimeType = response.mimeType,
        mimeType == "text/html" else {
        completionHandler(.cancel)
        return
    }
    completionHandler(.allow)
}

func urlSession(_ session: URLSession, dataTask: URLSessionDataTask, didReceive data: Data) {
    self.receivedData?.append(data)
}

func urlSession(_ session: URLSession, task: URLSessionTask, didCompleteWithError error: Error?) {
    DispatchQueue.main.async {
        self.loadButton.isEnabled = true
        if let error = error {
            handleClientError(error)
        } else if let receivedData = self.receivedData,
            let string = String(data: receivedData, encoding: .utf8) {
            self.webView.loadHTMLString(string, baseURL: task.currentRequest?.url)
        }
    }
}

https://developer.apple.com/documentation/foundation/url_loading_system/fetching_website_data_into_memory

===============================================

1.

12.If a download task completes successfully, then the NSURLSession object calls the task’s URLSession:downloadTask:didFinishDownloadingToURL: method with the location of a temporary file. Your app must either read the response data from this file or move it to a permanent location before this delegate method returns.

https://developer.apple.com/documentation/foundation/nsurlsession?language=objc

https://www.jianshu.com/p/8790684782c3

2.

后台任务完成操作

在切到后台之后，Session的Delegate不会再收到，Task相关的消息，直到所有Task全都完成后，系统会调用ApplicationDelegate的application:handleEventsForBackgroundURLSession:completionHandler:回调，把通知App后台Task已经完成，这里你需要completionHandler的bloack存起来下面会用到，接着每一个后台的Task就会调用Session的Delegate中的URLSession:downloadTask:didFinishDownloadingToURL:和URLSession:task:didCompleteWithError: 。

各个Task在Session的delegate调用之后，最后会调用Session的Delegate回调URLSessionDidFinishEventsForBackgroundURLSession:。这个时候你可以调用上面保存completionHandler的bloack，告知系统你的后台任务已经完成，系统可以安全的休眠你的App。

https://blog.csdn.net/hxming22/article/details/79392880

https://github.com/nsscreencast/093-background-transfers

3.

AFURLSessionManager

- (void)setDidFinishEventsForBackgroundURLSessionBlock:(void (^)(NSURLSession *session))block {
    self.didFinishEventsForBackgroundURLSession = block;
}
。。。
- (void)URLSessionDidFinishEventsForBackgroundURLSession:(NSURLSession *)session {
    if (self.didFinishEventsForBackgroundURLSession) {
        dispatch_async(dispatch_get_main_queue(), ^{
            self.didFinishEventsForBackgroundURLSession(session);
        });
    }
}