如何解决 - 组合错误 |错误域=NSURLErrorDomain 代码=-999 “已取消”答案

【问题标题】：How to resolve - Combine Error | Error Domain=NSURLErrorDomain Code=-999 "cancelled"如何解决 - 组合错误 |错误域=NSURLErrorDomain 代码=-999 “已取消”
【发布时间】：2020-02-22 03:48:52
【问题描述】：

我正在尝试使用新的 Combine 框架解析 JSON。但是，我所做的每一次尝试都会返回一个取消的错误。当我使用完全相同的网址而不使用组合时，它可以正常工作。

底部的功能正常，顶部的无论我做什么都会出错。

static func performNetworkRequestUsingCombine(url urlWithQuery:URL){
        //let decoder = JSONDecoder()
        let publisher = URLSession.shared.dataTaskPublisher(for: urlWithQuery)
            .map({$0.data})

        .eraseToAnyPublisher()
            .sink(receiveCompletion: { (status) in
                switch status {
                    case .failure(let incomingError):
                        print(incomingError.localizedDescription)
                    case .finished:
                    break
                }
            }) { (data) in
                let dataString = String(data: data, encoding: .utf8)
                print(dataString!)
        }
        publisher.cancel()
    }

static func performNetworkRequest(url urlWithQuery: URL, dataValue : @escaping (WeatherObject)->Void){

        let decoder = JSONDecoder()
        let task = URLSession.shared.dataTask(with: urlWithQuery) { (data, response, error) in

            if error != nil {
                print(error!.localizedDescription)
                return
            }
            if let data = data {
                do {
                    let weatherData = try decoder.decode(WeatherObject.self, from: data)
                    dataValue(weatherData)
                } catch let localError {
                    print(localError.localizedDescription)
                }
            }
        }
        task.resume()
    }

}

我希望收到打印在终端中的 JSON 数据，但我收到以下错误：

2019-10-25 14:59:34.452071-0400 Clima[2127:98883] 任务 . 完成错误 [-999] 错误域 = NSURLErrorDomain 代码 = -999 “取消” UserInfo={NSErrorFailingURLStringKey=https://api.openweathermap.org/data/2.5/weather?lon=-122.4&APPID=29ecd35ff6b9e63498cb8fb479ba6ca0&units=imperial&lat=37.8, NSLocalizedDescription=cancelled, NSErrorFailingURLKey=https://api.openweathermap.org/data/2.5/weather?lon=-122.4&APPID=29ecd35ff6b9e63498cb8fb479ba6ca0&units=imperial&lat=37.8}

【问题讨论】：

标签： ios swift xcode urlsession combine

【解决方案1】：

添加了 .receive(on:) 运算符，这解决了问题！

static func performNetworkRequestUsingCombine(url urlWithQuery:URL){
        //let decoder = JSONDecoder()

        let publisher = URLSession.shared.dataTaskPublisher(for: urlWithQuery)
            .map({$0.data})
            .receive(on: DispatchQueue.main)
            .sink(receiveCompletion: { (completionError) in
                switch completionError {
                    case .failure(let error):
                        print(error.localizedDescription)
                    case .finished:
                    break
                }
            }) { (data) in
                guard let stringData = String(data: data, encoding: .utf8) else {return}
                print(stringData)
        }
        publisher.cancel()
    }

【讨论】：