解码REST时Swift Playground中出现奇怪错误

如何解决解码REST时Swift Playground中出现奇怪错误

import Foundation
import Combine

let liveSample = URL(string: "https://newsapi.org/v2/top-headlines?country=us&apiKey=<api key>")!

struct ArticleList: Codable {
    struct Article: Codable {
        struct Source: Codable {
            var id: String?
            var name: String?
        }
        var source: Source?
        var author: String?
        var title: String?
        var description: String?
        var url: URL?
        var urlToImage: URL?
        var publishedAt: Date?
        var content: String?
    }
    var status: String
    var totalResults: Int
    var articles: [Article]
}

struct Resource<T: Codable> {
    let request: URLRequest
}

extension URLSession {
    func fetchJSON<T: Codable>(for resource: Resource<T>) -> AnyPublisher<T,Error> {
        return dataTaskPublisher(for: resource.request)
            .map { $0.data }
            .decode(type: T.self,decoder: JSONDecoder())
            .erasetoAnyPublisher()
    }
}

var subscriber: AnyCancellable?

var resource: Resource<ArticleList> =
    Resource<ArticleList>(request: URLRequest(url: liveSample))

subscriber?.cancel()
subscriber = URLSession.shared.fetchJSON(for: resource)
    .receive(on: dispatchQueue.main)
    .sink(receiveCompletion: { completion in
        switch completion {
        case .finished:
            print("The publisher finished normally.")
        case .failure(let error):
            print("An error occured: \(error).")
        }
    },receiveValue: { result in
        dump(result)
    })

我正在使用Xcode 12 RC生成错误：

发生错误：typeMismatch（Swift.Double，Swift.DecodingError.Context（codingPath：[CodingKeys（stringValue：“ articles”，intValue：nil），_JSONKey（stringValue：“ Index 0”，intValue：0），CodingKeys （stringValue：“ publishedAt”，intValue：nil）]，debugDescription：“预期对Double进行解码，但找到了一个字符串/数据。”，底层错误：nil））。

解决方法

我可以看到您在这里直接使用JSONDecoder()，在您的模型中var publishedAt: Date?是一个日期对象。

您需要先配置解码器以从字符串中解析日期，然后使用它。

let decoder = JSONDecoder()
decoder.dateDecodingStrategy = .iso8601 // <------- set date decoding strategy explicitly 
extension URLSession {
    func fetchJSON<T: Codable>(for resource: Resource<T>) -> AnyPublisher<T,Error> {
        return dataTaskPublisher(for: resource.request)
            .map { $0.data }
            .decode(type: T.self,decoder: decoder)
            .eraseToAnyPublisher()
    }
}