在Swift中，需要将Json数据转为实体时，一种简单的方式就是使用系统提供的JSONDecoder进行解码，这种方式需要实体类或结构体继承（实现）（java说法）一个类型别名（typealias）为Codable的东西。这个东西长这样：

/// A type that can convert itself into and out of an external representation.
///
/// `Codable` is a type alias for the `Encodable` and `Decodable` protocols.
/// When you use `Codable` as a type or a generic constraint, it matches
/// any type that conforms to both protocols.
public typealias Codable = Decodable & Encodable

简单使用

普通的类或结构体，直接继承Codable 就行了，可以不用做别的实现，要是属性中有引用别的类或结构体，需要这个属性也要继承Codable ，如下：

struct  NewsResponse :Codable {
    var code: Int
    var msg: String
    var result: ResultModel
    struct  ResultModel : Codable {
        var curpage: Int
        var allnum: Int
        var newslist: [ListModel]
        struct  ListModel : Codable {
            var id: String
            var ctime: String
            var title: String
            let description: String
            var source: String
            var picUrl: String
            var url: String
        }
    }
}

但是如果这个类或结构体的属性中有泛型的话，需要多做一些处理，不然会有编译时错误，如图：

需要多做一下处理：

也可以多做一些处理：

    init(code: Int?, data: T?, msg: String?) {
            self.code = code
            self.data = data
            self.msg = msg
    }

    init(from decoder: Decoder) throws {
        let container = try decoder.container(keyedBy: CodingKeys.self)
        code = try container.decode(Int.self, forKey: .code)
        data = try container.decode(T.self, forKey: .data)
        msg = try container.decode(String.self, forKey: .msg)
    }

    func encode(to encoder: Encoder) throws {
        var container = encoder.container(keyedBy: CodingKeys.self)
        try container.encode(code, forKey: .code)
        try container.encode(data, forKey: .data)
        try container.encode(msg, forKey: .msg)
    }

    private enum CodingKeys: String, CodingKey {
        case code
        case data
        case msg
    }

Json解析

然后就可以解析数据了：

do {
	let base = try JSONDecoder().decode(BaseBN<UserBN>.self, from: jsonData)
    let user=base.data
    if user != nil {
    	self.login(user: user!)
	}
    print(user as Any)
} catch {
  	print("Error decoding JSON: \(error)")
}