Swift 4 Decodable - 没有与键 CodingKeys 关联的值 [重复]

Posted 2023-02-18

【中文标题】Swift 4 Decodable - 没有与键 CodingKeys 关联的值 [重复]

【英文标题】：Swift 4 Decodable - No value associated with key CodingKeys [duplicate]

【发布时间】：2019-08-28 22:38:18

【问题描述】：

我正在我的 Swift 应用程序中解码 JSON 响应，并且代码在它决定停止工作之前一直有效。

这是我的 json 回复

    "foods": [
        
            "food_name": "Milk Chocolate",
            "brand_name": "Snickers",
            "serving_weight_grams": 41.7,
            "nf_calories": 212.3,
            "nf_total_fat": 11.6,
            "nf_saturated_fat": 4,
            "nf_total_carbohydrate": 22.7,
            "nf_protein": 3.9
        
    ]

这是解码我的 json 的代码

let task = URLSession.shared.dataTask(with: request)  (data, response, error) in
        guard let data = data else  return 
        
        print(String(data: data, encoding: .utf8)!)
        do 
            //Decode dataResponse received from a network request
            let decoder = JSONDecoder()
            let foods = try decoder.decode(JSONFoods.self, from: data) //Decode JSON Response Data
            
            self.jsonfood = foods.JSONFood[0]
            print(self.jsonfood!)
            
         catch let parsingError 
            print("Error", parsingError)
        
        
    
    task.resume()

我的结构是

struct JSONFoods: Decodable 
var JSONFood: [JSONFood]    


struct JSONFood: Decodable
var food_name: String
var brand_name: String
var nf_calories: Int
var nf_protein: Int
var nf_total_fat: Int
var nf_total_carbohydrate: Int
var serving_weight_grams: Int

我得到的错误信息是这样的

keyNotFound(CodingKeys(stringValue: "JSONFood", intValue: nil), Swift.DecodingError.Context(codingPath: [], debugDescription: "没有与键 CodingKeys 关联的值(stringValue: "JSONFood", intValue: nil) ( "JSONFood").", 底层错误：nil))

如果我将 decode(JSONFoods.self, from: data) 替换为 decode(JSONFood.self, from: data) 我收到此错误消息

keyNotFound(CodingKeys(stringValue: "food_name", intValue: nil), Swift.DecodingError.Context(codingPath: [], debugDescription: "没有与键 CodingKeys 关联的值(stringValue: "food_name", intValue: nil) ( "food_name").", 基础错误：nil))

我到处搜索都没有运气，非常感谢任何帮助

【问题讨论】：

JSONFood != foods.

【参考方案1】：

你需要

struct Root: Codable 
    let foods: [Food]


struct Food: Codable 
    let foodName: String?
    let  brandName: String
    let servingWeightGrams, nfCalories, nfTotalFat: Double
    let nfSaturatedFat: Int
    let nfTotalCarbohydrate, nfProtein: Double

    enum CodingKeys: String, CodingKey 
        case foodName = "food_name"
        case brandName = "brand_name"
        case servingWeightGrams = "serving_weight_grams"
        case nfCalories = "nf_calories"
        case nfTotalFat = "nf_total_fat"
        case nfSaturatedFat = "nf_saturated_fat"
        case nfTotalCarbohydrate = "nf_total_carbohydrate"
        case nfProtein = "nf_protein"
    

首先：你应该是JSONFood，而它应该是foods

第二个：food_name 在当前的 json 根目录中不存在，所以这会失败

let foods = try decoder.decode(JSONFoods.self, from: data) //Decode JSON Response Data

---

万一利用convertFromSnakeCase

let str = """

"foods":["food_name":"Milk Chocolate","brand_name":"Snickers","serving_weight_grams":41.7,"nf_calories":212.3,"nf_total_fat":11.6,"nf_saturated_fat":4,"nf_total_carbohydrate":22.7,"nf_protein":3.9]

"""

    do 
        let res = JSONDecoder()
        res.keyDecodingStrategy = .convertFromSnakeCase
        let ss = try res.decode(Root.self, from:Data(str.utf8))
        print(ss)
    
    catch 
        print(error)
    

---

struct Root: Codable 
    let foods: [Food]


struct Food: Codable 
    let foodName: String?
    let  brandName: String
    let servingWeightGrams, nfCalories, nfTotalFat: Double
    let nfSaturatedFat: Int
    let nfTotalCarbohydrate, nfProtein: Double

【讨论】：

不需要将JSONFoods结构重命名为Root。

我会这样做，以防有多个结构用于突出显示基本模型

出现问题中的第二个错误是因为 OP 将子结构 JSONFood 解码为根对象。 food_name 可能丢失与此无关。为什么不建议.convertFromSnakeCase 策略来摆脱CodingKeys？

我只是在评论之前编辑它:)，是的，我同意蛇案例更好，但动态站点生成现在可能不会考虑它=D