在 Swift 中序列化 JSON 4 - 确定数据类型时出现问题

Question

我正在从网上 API 抓取一些 JSON 并将结果放入数组以备将来使用。到目前为止所有数据都很好（只是字符串数组），但我不知道如何处理其中一个结果。

This is the JSON (someone advised that I use https://jsonlint.com 使其可读且非常有用）

这是获取 JSON:

的函数

func getJSON(completionHandler: @escaping (Bool) -> ()) {
    let jsonUrlString = "https://api.nytimes.com/svc/topstories/v1/business.json?api-key=f4bf2ee721031a344b84b0449cfdb589:1:73741808"
    guard let url = URL(string: jsonUrlString) else {return}

    URLSession.shared.dataTask(with: url) { (data, response, err) in
        guard let data = data, err == nil else {
            print(err!)
            return
        }

        do {
            let response = try
                JSONDecoder().decode(TopStoriesResponse.self, from: data)

            // Pass results into arrays (title, abstract, url, image)
            for result in response.results {
                let headlines = result.title
                let abstracts = result.abstract
                let url = result.url

                self.headlines.append(headlines)
                self.abstracts.append(abstracts)
                self.urls.append(url)
            }

            let imageResponse = try
                JSONDecoder().decode(Story.self, from: data)
            for imageResults in imageResponse.multimedia {
                let images = imageResults.url
                self.images.append(images)
            }

            completionHandler(true)


        } catch let jsonErr {
            print("Error serializing JSON", jsonErr)
        }
    }.resume()
}

这些是用于序列化 JSON:

的结构

struct TopStoriesResponse: Decodable {
    let status: String
    let results: [Story]
}

struct Story: Decodable {
    let title: String
    let abstract: String
    let url: String
    let multimedia: [Multimedia]
}

struct Multimedia: Codable {
    let url: String
    let type: String
}

我将结果组织到这些数组中：

var headlines = [String]()
var abstracts = [String]()
var urls = [String]()
var images = [String]()

我在viewDidLoad

中调用函数

getJSON { (true) in
    print("Success")
    print("\n\nHeadlines: \(self.headlines)\n\nAbstracts: \(self.abstracts)\n\nURLS: \(self.urls)\n\nImages: \(self.images)")
}

正如您在 getJSON 函数中看到的那样，我尝试使用

获取图像

let imageResponse = try JSONDecoder().decode(Story.self, from: data)
for imageResults in imageResponse.multimedia {
    let images = imageResults.url
    self.images.append(images)
}

但是我收到错误

CodingKeys(stringValue: "multimedia", intValue: nil)], debugDescription: "Expected to decode Array but found a string/data instead.", underlyingError: nil))

我很困惑，因为它说它期待一个数组，但却找到了一个字符串 - 图像不是数组吗，就像 headlines、abstracts 等？

Answer 1

您已将 multimedia 定义为数组。 json 中有些部分没有任何多媒体，设置为空字符串：

multimedia: ""

您需要能够处理任何一种情况。由于 Codable 旨在处理具体类型，因此您最好改用 JSONSerialization。

如果你非常喜欢使用Codable，你可以操作字符串形式的JSON响应，将multimedia: ""转换成你期望的格式，然后传递给解码器。例如，您可以将多媒体设为可选，只需删除带有 multimedia: "".

的任何行

Answer 2

问题是 multimedia 是 Multimedia 个对象的数组或空的 String。您需要为 Story 编写自定义初始化程序来处理它。

struct Story: Decodable {
    let title: String
    let abstract: String
    let url: String
    let multimedia: [Multimedia]

    private enum CodingKeys: String, CodingKey {
        case title
        case abstract
        case url
        case multimedia
    }

    init(from decoder:Decoder) throws {
        let container = try decoder.container(keyedBy: CodingKeys.self)
        title = try container.decode(String.self, forKey: .title)
        abstract = try container.decode(String.self, forKey: .abstract)
        url = try container.decode(String.self, forKey: .url)
        multimedia = (try? container.decode([Multimedia].self, forKey: .multimedia)) ?? []
    }
}

Answer 3

问题在于来自服务器的 JSON 响应，Multimedia 数组在 JSON 响应之一中显示为空 "" String。要处理这种情况，您需要手动实现 init(from decoder:) 方法并处理空字符串的情况。此外，您不需要创建单独的数组来存储值，您可以直接在完成处理程序闭包中传递 TopStoriesResponse 结构，并在需要时在 ViewController 中获取值。

假设您创建了一个包含成功 (T) 和失败 (错误) 的结果枚举，并将其传递到您的 completionHandler 中供 ViewController 处理

enum Result<T> {
    case success(T)
    case failure(Error)
}

struct Networking {

    static func getJson(completionHandler: @escaping (Result<TopStoriesResponse>) -> ()) {

        let jsonUrlString = "https://api.nytimes.com/svc/topstories/v1/business.json?api-key=f4bf2ee721031a344b84b0449cfdb589:1:73741808"

        guard let url = URL(string: jsonUrlString) else {
            return
        }

        URLSession.shared.dataTask(with: url) { (data, response, error) in

            guard let data = data, error == nil else {
                completionHandler(Result.failure(error!))
                return
            }

            do {
                let topStoriesResponse: TopStoriesResponse = try JSONDecoder().decode(TopStoriesResponse.self, from: data)
                print(topStoriesResponse.results.count)
                completionHandler(Result.success(topStoriesResponse))
            } catch {
                completionHandler(Result.failure(error))
            }
        }.resume()
    }
}

现在在您的 ViewController 中您可以调用 getJson 方法并切换 completionHandler 中的结果枚举以获取值

class ViewController: UIViewController {

    var topStories: TopStoriesResponse?

    override func viewDidLoad() {
        super.viewDidLoad()
        loadData()
    }

    func loadData() {
        Networking.getJson { (result: Result<TopStoriesResponse>) in
            switch result {
            case let .success(topStories):
                self.topStories = topStories

                topStories.results.forEach({ (story: Story) in
                    print("Title: \(story.title) \n Abstracts = \(story.abstract)  URL = \(story.url)")
                })
                //reload tableView
            case let .failure(error):
                print(error.localizedDescription)
            }
        }
    }
}

要处理空字符串的情况，您需要在多媒体结构中实现 init(decoder:) 方法，如上所述

struct Multimedia: Decodable {
    let url: String
    let image: String
    let height: Float
    let width: Float
}

struct Story: Decodable {
    let title: String
    let abstract: String
    let url: String
    let multimedia: [Multimedia]

    private enum CodingKeys: String, CodingKey {
        case title
        case abstract
        case url
        case multimedia
    }

    init(from decoder:Decoder) throws {
        let container = try decoder.container(keyedBy: CodingKeys.self)
        title = try container.decode(String.self, forKey: .title)
        abstract = try container.decode(String.self, forKey: .abstract)
        url = try container.decode(String.self, forKey: .url)
        multimedia = (try? container.decode([Multimedia].self, forKey: .multimedia)) ?? []
    }
}

struct TopStoriesResponse: Decodable {
    let status: String
    let copyright: String
    let num_results: Int
    let results: [Story]
}

在 Swift 中序列化 JSON 4 - 确定数据类型时出现问题

Serializing JSON in Swift 4 - problem figuring out data type

json

swift

codable