Swift 4序列化json类型不匹配时出错

Question

我试图将数据从静态JSON文件解析到我的实体，但我得到了以下错误：Error serializing json typeMismatch

这个想法是创建一个配方收集应用程序。每次应用程序启动时，都应该通过加载JSON来加载公式集合。这样可以更容易地更新公式列表。

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()
}

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

您的主要问题是声明类型以解析此JSON。

这里没有CategoryList，它可能类似于：

{
"data": [ … <Category JSON> … ]
}

这里只有[Category]，就像JSON根是Array([](，而不是Object({}(一样。

所以不是

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

你应该做

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

---

此外，如果您的编码键与JSON中的键几乎相同，但与snake情况不同，则不应为您的类型声明自定义CodingKey。请改用正确的.keyDecodingStrategy。

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)