如何在 Swift 中使用自定义解码器初始化和递增键来解析 JSON答案

【问题标题】：How to parse JSON using custom decoder init with incrementing keys in Swift如何在 Swift 中使用自定义解码器初始化和递增键来解析 JSON
【发布时间】：2020-10-08 15:32:24
【问题描述】：

我有一些餐点 json，我想将其转换为 MealData 结构

let randomMealJson = """
{
    "meals": [{
        "idMeal": "52812",
        "strMeal": "Beef Brisket Pot Roast",
        "strDrinkAlternate": null,
        "strCategory": "Beef",
        "strArea": "American",
        "strInstructions": "Meal instructions",
        "strMealThumb": "https://www.themealdb.com/images/media/meals/ursuup1487348423.jpg",
        "strTags": "Meat",
        "strYoutube": "https://www.youtube.com/watch?v=gh48wM6bPWQ",
        "strIngredient1": "Beef Brisket",
        "strIngredient2": "Salt",
        "strIngredient3": "Onion",
        "strIngredient4": "Garlic",
        "strIngredient5": "Thyme",
        "strIngredient6": "Rosemary",
        "strIngredient7": "Bay Leaves",
        "strIngredient8": "beef stock",
        "strIngredient9": "Carrots",
        "strIngredient10": "Mustard",
        "strIngredient11": "Potatoes",
        "strIngredient12": null,
        "strIngredient13": null,
        "strIngredient14": null,
        "strIngredient15": null,
        "strIngredient16": null,
        "strIngredient17": null,
        "strIngredient18": null,
        "strIngredient19": null,
        "strIngredient20": null,
        "strMeasure1": "4-5 pound",
        "strMeasure2": "Dash",
        "strMeasure3": "3",
        "strMeasure4": "5 cloves",
        "strMeasure5": "1 Sprig",
        "strMeasure6": "1 sprig ",
        "strMeasure7": "4",
        "strMeasure8": "2 cups",
        "strMeasure9": "3 Large",
        "strMeasure10": "1 Tbsp",
        "strMeasure11": "4 Mashed",
        "strMeasure12": "",
        "strMeasure13": "",
        "strMeasure14": "",
        "strMeasure15": "",
        "strMeasure16": "",
        "strMeasure17": "",
        "strMeasure18": "",
        "strMeasure19": "",
        "strMeasure20": "",
        "strSource": "http://www.simplyrecipes.com/recipes/beef_brisket_pot_roast/",
        "dateModified": null
    }]
}
"""

这是我想要制作的结构...

struct MealData: Decodable {
    let meals: [Meal]
}

struct Meal: Decodable {
    let items: [Item]
}

extension Meal {
    struct Item: Decodable {
        let ingredient: String
        let measure: String
    }
}

extension Meal {
    init(from decoder: Decoder) throws {
//        var items: [Item] = (0...20).map { num in      
//           what to do here?
//        }
    }
}

我想检查成分和措施，并从中创建一个Meal.Item，但我不知道如何实现这一点。可以按照我在代码中指出的方式吗？

【问题讨论】：

标签： json swift decodable

【解决方案1】：

我会分两步完成。先解码成字典

struct MealData: Decodable {
    let meals: [[String: String?]]
}

然后我会在单独的步骤中转换为另一种类型

struct Recipie {
    var ingredients: [Ingredient]
}

struct Ingredient {
    let ingredient: String
    let measure: String
}

这是完整的代码

do {
    let result = try JSONDecoder().decode(MealData.self, from: randomMealJson)

    var recipies = [Recipie]()
    for meal in result.meals {
        var recipie = Recipie(ingredients: [])
        var index = 1
        while true {
            guard let ingredientValue = meal["strIngredient\(index)"],
                  let measureValue = meal["strMeasure\(index)"],
                  let ingredient = ingredientValue,
                  let measure = measureValue, !measure.isEmpty
            else { break }

            recipie.ingredients.append(Ingredient(ingredient: ingredient, measure: measure))
            recipies.append(recipie)
            index += 1
        }
    }
} catch {
    print(error)
}

【讨论】：

【解决方案2】：

按照@joakim-danielson 的回答。你可以在 init(from:) 初始化器中做同样的事情，就像你的初衷一样。

只需将每个Meal 的成分和度量解码为[String: String?] 并编写您的自定义Items：

extension Meal {
    init(from decoder: Decoder) throws {
        let container = try decoder.singleValueContainer()
        
        let mealDict = try container.decode([String: String?].self)
        var index = 1
        var items = [Item]()
        while
            let ingredient = mealDict["strIngredient\(index)"] as? String,
            let measure = mealDict["strMeasure\(index)"] as? String,
            !measure.isEmpty
        {
            items.append(Item(ingredient: ingredient, measure: measure))
            index += 1
        }
        self.items = items
    }
}

【讨论】：