swift - 如何在 Swift 4 中使用 JSONEncoder 对字典进行编码

Question

我想用 JSONEncoder 将字典编码为 json。它看起来像一个请求，接收一个字典作为参数并将其编码为 json 作为 http 主体。代码如下所示:

let dict = ["name": "abcde"]

protocol Request {
    var params: [String: Encodable] { get set }
    func encode<T>(_ value: T) throws -> Data where T : Encodable
}

extension Request {
    func encode<T>(_ value: T) throws -> Data where T : Encodable {
        return try JSONEncoder().encode(value)
    }

    var body: Data? {
        if let encoded = try? self.encode(self.params) {
            return encoded
        }
        return nil
    }
}

struct BaseRequest: Request {
    var params: [String : Encodable]
}

let req = BaseRequest(params: dict)
let body = req.body

但是这段代码出现错误

Fatal error: Dictionary<String, Encodable> does not conform to Encodable because Encodable does not conform to itself. You must use a concrete type to encode or decode.

我怎样才能使它可编码？

Answer 1

你必须按如下方式引入类型删除:

struct AnyEncodable: Encodable {

    let value: Encodable
    init(value: Encodable) {
        self.value = value
    }

    func encode(to encoder: Encoder) throws {
        try value.encode(to: encoder)
    }

}

struct Model: Encodable {

    var params: [String: AnyEncodable]

}

let encoder = JSONEncoder()
encoder.outputFormatting = .prettyPrinted
let json = try! encoder.encode(
    Model(
        params: [
            "hello" : AnyEncodable.init(value: "world")
        ]
    ).params
)
print(String(data: json, encoding: .utf8))