swift - 如何使用 Codable 解析不同对象列表的 Json 数组?
问题描述
我有一个带有项目列表的 json 数组,它具有不同的属性。
{
"items": [
{
"id": "1",
"name": "name",
"propertyOfA": "1243",
"productype": "a"
},
{
"id": "2",
"name": "name",
"propertyOfA": "12",
"productype": "a"
},
{
"id": "3",
"name": "name",
"propertyOfA": "1243",
"productype": "a"
},
{
"id": "1",
"name": "name",
"propertyOfB": "1243",
"productype": "b"
},
{
"id": "1",
"name": "name",
"propertyOfC": "1243",
"propertyOfC2": "1243",
"productype": "c"
}
]
}
我通常做的是将其解析为:
struct RequestData: Codable {
let items: [Item]
}
enum ProductType: String, Codable {
case a = "A"
case b = "B"
case c = "C"
}
struct Item: Codable {
let id, name: String
let propertyOfA: String?
let productype: String
let propertyOfB: String?
let propertyOfC: String?
let propertyOfC2: String?
}
但是如果这个数组继续增长,它最终会得到一个具有大量可选属性的 Item,所以我希望每个对象都有自己的专用类
在可编码解析中添加某种桥梁,
我要存档的内容类似于:
struct RequestData: Codable {
let items: Items
}
struct items: Codable {
let arrayA: [A]
let arrayB = [B]
let arrayC = [C]
}
struct A: Codable {
let id: String,
let name: String,
let propertyOfA: String,
let producttype: Productype
}
struct B {
...
}
struct C {
...
}
我可以用 Codable 做到这一点吗?
解决方案
一个合理的解决方案是一个带有关联值的枚举,因为类型可以由productype
键确定。该init
方法首先productype
用 a 解码 aCodingKey
然后switch
它解码(从 a singleValueContainer
)并将正确的类型/值与相应的情况相关联。
enum ProductType: String, Codable {
case a, b, c
}
struct Root : Codable {
let items : [Product]
}
struct ProductA : Codable {
let id, name: String
let productype: ProductType
let propertyOfA : String
}
struct ProductB : Codable {
let id, name: String
let productype: ProductType
let propertyOfB : String
}
struct ProductC : Codable {
let id, name: String
let productype: ProductType
let propertyOfC, propertyOfC2 : String
}
enum Product : Codable {
case a(ProductA), b(ProductB), c(ProductC)
enum CodingKeys : String, CodingKey { case productype }
init(from decoder: Decoder) throws {
let container = try decoder.container(keyedBy: CodingKeys.self)
let type = try container.decode(ProductType.self, forKey: .productype)
let singleContainer = try decoder.singleValueContainer()
switch type {
case .a : self = .a(try singleContainer.decode(ProductA.self))
case .b : self = .b(try singleContainer.decode(ProductB.self))
case .c : self = .c(try singleContainer.decode(ProductC.self))
}
}
func encode(to encoder: Encoder) throws {
var container = encoder.singleValueContainer()
switch self {
case .a(let productA): try container.encode(productA)
case .b(let productB): try container.encode(productB)
case .c(let productC): try container.encode(productC)
}
}
}
并解码
let jsonString = """
{
"items": [
{
"id": "1",
"name": "name",
"propertyOfA": "1243",
"productype": "a"
},
{
"id": "2",
"name": "name",
"propertyOfA": "12",
"productype": "a"
},
{
"id": "3",
"name": "name",
"propertyOfA": "1243",
"productype": "a"
},
{
"id": "1",
"name": "name",
"propertyOfB": "1243",
"productype": "b"
},
{
"id": "1",
"name": "name",
"propertyOfC": "1243",
"propertyOfC2": "1243",
"productype": "c"
}
]
}
"""
do {
let result = try JSONDecoder().decode(Root.self, from: Data(jsonString.utf8))
print(result)
} catch { print(error)}
要读取枚举值,还可以使用switch
.