json - Swift 4 序列化 json 时出错 typeMismatch

Question

我正在尝试将数据从静态 JSON 文件解析到我的实体，但出现以下错误:序列化 json typeMismatch 时出错

这个想法是创建一个公式收集应用程序。每次应用程序启动时都应通过加载 JSON 来加载公式集合。这样可以更轻松地更新公式列表。

我猜 JSON 解释了预期的数据结构。

我的 JSON:

[
    {
        "category_name": "Wasserbau",
        "icon": "wave",
        "formula_list": [
            {
                "formula_name": "Formel 1",
                "formula_description": "Demo Formel für Testat",
                "formula": "x=y/z",
                "favorite": false
            },
            {
                "formula_name": "Formel 2",
                "formula_description": "Demo Formel für Testat",
                "formula": "x=y/z",
                "favorite": false
            }
        ]
    },
    {
        "category_name": "Strassenbau",
        "icon": "wave",
        "formula_list": [
            {
                "formula_name": "Formel 3",
                "formula_description": "Demo Formel für Testat",
                "formula": "x=y/z",
                "favorite": false
            },
            {
                "formula_name": "Formel 4",
                "formula_description": "Demo Formel für Testat",
                "formula": "x=y/z",
                "favorite": false
            }
        ]
    },
    {
        "category_name": "Hochbau",
        "icon": "wave",
        "formula_list": [
            {
                "formula_name": "Formel 5",
                "formula_description": "Demo Formel für Testat",
                "formula": "x=y/z",
                "favorite": false
            },
            {
                "formula_name": "Formel 6",
                "formula_description": "Demo Formel für Testat",
                "formula": "x=y/z",
                "favorite": false
            }
        ]
    }
]

我尝试解析 JSON 的函数:

 func loadCategoryJSONData() {
        let jsonUrlString = "https://joshuahemmings.ch/data.json"

        guard let url = URL(string: jsonUrlString) else {return} //
        URLSession.shared.dataTask(with: url) { (data, response, err) in
            guard let data = data else {return}
            print("JSON Response: ")
            print(data)
            do {
                let categoryJSONData =  try JSONDecoder().decode(CategoryList.self, from: data)
                for category in categoryJSONData.data {
                    print(category.categoryName)
                }
            } catch let jsonErr {
                print("Error serializing json", jsonErr)
            }
            }.resume()
    }

还有我的实体:

struct CategoryList: Decodable {
        let data: [Category]
    }

    struct Formula: Codable {
        let formulaName : String
        let formulaDescription : String
        let formula : String
        let favorite: Bool

        enum CodingKeys: String, CodingKey {
            case formulaName = "formula_name"
            case formulaDescription = "formula_description"
            case formula
            case favorite
        }
        init(_ dictionary: [String: Any]) {
            self.formulaName = dictionary["formulaName"] as? String ?? ""
            self.formulaDescription = dictionary["formulaDescription"] as? String ?? ""
            self.formula = dictionary["formula"] as? String ?? ""
            self.favorite = dictionary["favorite"] as? Bool ?? false
        }
    }

    struct Category: Codable {
        let categoryName: String
        let icon: String
        let formulaList: [Formula]

        enum CodingKeys: String, CodingKey {
            case categoryName = "category_name"
            case icon = "icon"
            case formulaList = "formula_list"
        }

        init(_ dictionary: [String: Any]) {
            self.categoryName = dictionary["categoryName"] as? String ?? ""
            self.icon = dictionary["icon"] as? String ?? ""
            self.formulaList = dictionary["formulaList"] as? [Formula] ?? []
        }
    }

Answer 1

您的主要问题在于声明类型来解析此 JSON。

这里没有CategoryList，它会是这样的:

{
    "data": [ … <Category JSON> … ]
}

这里只有 [Category]，就像 JSON 根是 Array([])，而不是 Object({})。

所以而不是

try decoder.decode(CategoryList.self, from: data)

你应该这样做

try decoder.decode([Category].self, from: data)

<小时/>

此外，如果您的编码键与 JSON 中的键几乎相同，但不是蛇形格式，则不应为您的类型声明自定义 CodingKey。正确使用.keyDecodingStrategy相反。

struct Formula: Codable {
    let formulaName: String
    let formulaDescription: String
    let formula: String
    let favorite: Bool
}

struct Category: Codable {
    let categoryName: String
    let icon: String
    let formulaList: [Formula]
}

let decoder = JSONDecoder()
decoder.keyDecodingStrategy = .convertFromSnakeCase
let categoryJSONData =  try decoder.decode([Category].self, from: data)