如何使用 Swift 中的对象数组解析 JSON 文件？

Question

几个小时以来，我一直在尝试使用数组解析 JSON 文件以试验 API，但我不断收到错误。我设法只用一个 JSON object/dictionary 解析一个文件（按照不同的教程），但我无法弄清楚一个包含对象数组的 JSON 文件。我正在用冠状病毒 API 对此进行测试。这是 URL，因此您可以看到 JSON 代码：https://coronavirus-19-api.herokuapp.com/countries。我觉得解决方案非常简单，只是缺少一些小东西，但我不太确定。

这是我得到的错误：

valueNotFound(Swift.Int, Swift.DecodingError.Context(codingPath: [_JSONKey(stringValue: "Index 10", intValue: 10), CodingKeys(stringValue: "recovered", intValue: nil)], debugDescription: "Expected Int value but found null instead.", underlyingError: nil))

这是我的代码：

import UIKit

class FirstViewController: UIViewController {
    
    var coronaInfo = [CoronaInfo]()
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        let url = "https://coronavirus-19-api.herokuapp.com/countries"
        
        getData(from: url) { (data) in
            self.coronaInfo = data
            print(self.coronaInfo[0].cases)   // <-- Works in here
        }
        
        print(coronaInfo[0].cases) // <-- Outside of the closure it's nil
    }
    
    func getData(from url: String, completed: @escaping ([CoronaInfo]) -> ()) {
        URLSession.shared.dataTask(with: URL(string: url)!) { data, response, error in
            // Make sure that data isn't nil and that there was no error
            guard let data = data, error == nil else { print("Something went wrong"); return }
            
            var result: [CoronaInfo]?
            do {
                // Convert data from bytes to the custom object (Known as JSON decoding)
                result = try JSONDecoder().decode([CoronaInfo].self, from: data)
                
                guard let json = result else { return }
                
                DispatchQueue.main.async {
                    completed(json)
                }
            } catch { print(error) }
            
        }.resume()
    }

}

struct CoronaInfo: Codable {
    let country: String
    let cases: Int
    let todayCases: Int
    let deaths: Int
    let todayDeaths: Int
    let recovered: Int?
    let active: Int?
    let critical: Int
    let casesPerOneMillion: Int
    let deathsPerOneMillion: Int
    let totalTests: Int
    let testsPerOneMillion: Int
}

在此先感谢您的帮助！

Answer 1

这里有两点值得一提

您尝试解析的响应应该来自 https://coronavirus-19-api.herokuapp.com/countries not from https://corona-virus-stats.herokuapp.com/api/v1/cases/general-stats。所以使用第一个 link 而不是第二个

        let url = "https://coronavirus-19-api.herokuapp.com/countries"
        getData(from: url)

由于有两个字段具有 null 值，请在您的模型中将它们标记为可选。

struct CoronaData: Codable {
    let country: String
    let cases: Int
    let todayCases: Int
    let deaths: Int
    let todayDeaths: Int
    let recovered: Int?
    let active: Int?
    let critical: Int
    let casesPerOneMillion: Int
    let deathsPerOneMillion: Int
    let totalTests: Int
    let testsPerOneMillion: Int
}

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