在Swift中动态解码任意json字段-Java 学习之路

TL;DR

有没有办法我可以使用 JSONDecoder 并编写一个函数，它将从指定的可解码类型给定的json给定字段值读出？

成像我有以下json：

{
   "product":{
      "name":"PR1",
      "price":20
   },
   "employee":{
      "lastName":"Smith",
      "department":"IT",
      "manager":"Anderson"
   }
}

我有2个 Decodable 结构：

struct Product: Decodable {
    var name: String
    var price: Int
}

struct Employee: Decodable {
    var lastName: String
    var department: String
    var manager: String
}

我想写一个函数

func getValue<T:Decodable>(from json: Data, field: String) -> T { ... }

所以我可以这么称呼它：

let product = getValue<Product>(from: myJson, field: "product")
let employee = getValue<Employee>(from: myJson, field: "employee")

这可能是 JSONDecoder 或者我应该使用 JSONSerialization ，首先读出给定json的"subtree"然后将其传递给解码器？在swift中似乎不允许在泛型函数中定义结构 .

2 回答

Decodable 假设您在设计时知道您想要的所有内容以启用静态类型 . 您想要的动态越多，您就越有创意 . 在这种情况下，定义通用编码键结构非常方便：

/// A structure that holds no fixed key but can generate dynamic keys at run time
struct GenericCodingKeys: CodingKey {
    var stringValue: String
    var intValue: Int?

    init?(stringValue: String) { self.stringValue = stringValue }
    init?(intValue: Int) { self.intValue = intValue; self.stringValue = "\(intValue)" }
    static func makeKey(_ stringValue: String) -> GenericCodingKeys { return self.init(stringValue: stringValue)! }
    static func makeKey(_ intValue: Int) -> GenericCodingKeys { return self.init(intValue: intValue)! }
}

/// A structure that retains just the decoder object so we can decode dynamically later
fileprivate struct JSONHelper: Decodable {
    let decoder: Decoder

    init(from decoder: Decoder) throws {
        self.decoder = decoder
    }
}

func getValue<T: Decodable>(from json: Data, field: String) throws -> T {
    let helper = try JSONDecoder().decode(JSONHelper.self, from: json)
    let container = try helper.decoder.container(keyedBy: GenericCodingKeys.self)
    return try container.decode(T.self, forKey: .makeKey(field))
}

let product: Product = try getValue(from: json, field: "product")
let employee: Employee = try getValue(from: json, field: "employee")

回复于 2024-04-27T22:59:46+08:00

我建议使用Code Different's answer，但是如果你寻求一种不同的方式，那么在表面下以相同的方式工作，我已经扩展了他们的解决方案，导致下面的代码 .

我也会推荐这些：

/// Conforming to this protocol, makes the type decodable using the JSONContainer class
protocol ContainerCodable: Codable {
    static var containerIdentifier: String { get }
}

extension ContainerCodable {
    static var containerIdentifier: String {
        return String(describing: self).lowercased()
    }
}

struct Product: ContainerCodable {

    var name:  String
    var price: Int
}

struct Employee: ContainerCodable {

    var lastName:   String
    var department: String
    var manager:    String
}

class JSONContainer: Decodable {

    private struct AnyCodingKeys: CodingKey {

        var stringValue: String
        var intValue: Int?

        init?(intValue: Int) {
            self.intValue = intValue
            self.stringValue = "\(intValue)"
        }

        init?(stringValue: String) {
            self.stringValue = stringValue
        }

        init(_ string: String) {
            self.init(stringValue: string)!
        }
    }

    private let decoder: JSONDecoder
    private let container: KeyedDecodingContainer<AnyCodingKeys>

    required init(from decoder: Decoder) throws {
        self.decoder = JSONDecoder()
        self.container = try decoder.container(keyedBy: AnyCodingKeys.self)
    }

    static func decoding(_ data: Data) throws -> JSONContainer {
        let decoder = JSONDecoder()
        return try decoder.decode(JSONContainer.self, from: myJSON)
    }

    func get<T: ContainerCodable>(_ type: T.Type) throws -> T {
        return try container.decode(T.self, forKey: AnyCodingKeys(T.containerIdentifier))
    }

    func get<T: ContainerCodable>() throws -> T {
        return try get(T.self)
    }
}

let myJSON = """
{
    "product": {
        "name": "PR1",
        "price": 20
    },
    "employee": {
        "lastName": "Smith",
        "department": "IT",
        "manager": "Anderson"
    }
}
""".data(using: .utf8)!

let container = try! JSONContainer.decoding(myJSON)

print(try! container.get( Product.self))
print(try! container.get(Employee.self))

Product(name: "PR1", price: 20)
Employee(lastName: "Smith", department: "IT", manager: "Anderson")

回复于 2024-04-27T22:59:46+08:00

在Swift中动态解码任意json字段

2 回答

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