编辑/更新：Swift 4或更高版本，您可以使用可编码协议：

struct Root: Codable {
    let user: User
    let address: Address
    let deliveryInstruction, deliveryMethod: String
}

struct Address: Codable {
    let house, street, addressId, fullAddress: String
    let town: Town
    let city: City
}

struct City: Codable {
    let cityId, cityName: String
}

struct Town: Codable {
    let townId, townName: String
}

struct User: Codable {
    let name, email, phoneNo: String
}

extension Decodable {
    init(data: Data, using decoder: JSONDecoder = .init()) throws {
        self = try decoder.decode(Self.self, from: data)
    }
    init(json: String, using decoder: JSONDecoder = .init()) throws {
        try self.init(data: Data(json.utf8), using: decoder)
    }
}

只是不要忘记将JSONDecoder属性设置keyDecodingStrategy为.convertFromSnakeCase：

let json = """
{"user": {"name": "crst","email": "crat@gmail.com","phoneNo":"018833455"},"address": {"house": "100","street": "B","town":{"town_id": "1","town_name": "Galway city center"},"city":{"city_id": "10","city_name": "Galway"},"address_id":"200", "full_address":"100, B, Galway city center,Galway" },"delivery_instruction": "no call","delivery_method": "1" }
"""

do {
    let decoder = JSONDecoder()
    decoder.keyDecodingStrategy = .convertFromSnakeCase
    let root = try decoder.decode(Root.self, from: Data(json.utf8))
    print(root)
} catch {
    print(error)
}

或者简单地：

do {
    let decoder = JSONDecoder()
    decoder.keyDecodingStrategy = .convertFromSnakeCase
    let root = try Root(json: json, using: decoder)  // or  Root(data: data, using: decoder) 
    print(root)
} catch {
    print(error)
}

这将打印

根（用户： lldb_expr_112.User（名称：“ cruskuaka”，电子邮件：“
cristlika@gmail.com”，电话号码：“ 018833455”）），地址： lldb_expr_112.Address（房屋：“
100”，街道：“ B”，addressId ：“ 200”，完整地址：“ 100，B，戈尔韦市中心，戈尔韦”，镇：
lldb_expr_112.Town（townId：“ 1”，townName：“戈尔韦市中心”），城市：
lldb_expr_112.City（cityId：“ 10 “，cityName：” Galway“）），deliveryInstruction：”
no call“，deliveryMethod：” 1“）

原始答案（在可编码协议之前）

迅捷3

您的代码中有多个错误，但您所走的路正确。初始化用户，城市和城镇结构时使用的密钥错误。我还创建了另外两个初始化程序，因此您可以使用字典，json字符串或仅其数据初始化结构：

struct Contact: CustomStringConvertible  {
    let user: User
    let address: Address
    let deliveryInstruction: String
    let deliveryMethod: String
    // customize the description to your needs
    var description: String { return "\(user.name) \(deliveryInstruction) \(deliveryMethod)" }
    init(dictionary: [String: Any]) {
        self.deliveryInstruction = dictionary["delivery_instruction"] as? String ?? ""
        self.deliveryMethod = dictionary["delivery_method"] as? String ?? ""
        self.address = Address(dictionary: dictionary["address"] as? [String: Any] ?? [:])
        self.user =  User(dictionary: dictionary["user"] as? [String: Any] ?? [:])
    }
    init?(data: Data) {
        guard let json = (try? JSONSerialization.jsonObject(with: data)) as? [String: Any] else { return nil }
        self.init(dictionary: json)
    }
    init?(json: String) {
        self.init(data: Data(json.utf8))
    }

}

struct User: CustomStringConvertible {
    let name: String
    let email: String
    let phone: String
    let description: String
    init(dictionary: [String: Any]) {
        self.name = dictionary["name"] as? String ?? ""
        self.email = dictionary["email"] as? String ?? ""
        self.phone = dictionary["phoneNo"] as? String ?? ""
        self.description = "name: \(name) - email: \(email) - phone: \(phone)"
    }
}

struct Address: CustomStringConvertible  {
    let id: String
    let street: String
    let house: String
    let city: City
    let town: Town
    let description: String
    init(dictionary: [String: Any] ) {
        self.id = dictionary["address_id"] as? String ?? ""
        self.description = dictionary["full_address"] as? String ?? ""
        self.house = dictionary["house"] as? String ?? ""
        self.street = dictionary["street"] as? String ?? ""
        self.city = City(dictionary: dictionary["city"] as? [String: Any] ?? [:])
        self.town = Town(dictionary: dictionary["town"] as? [String: Any] ?? [:])
    }
}

struct City: CustomStringConvertible {
    let id: String
    let name: String
    // customize the description to your needs
    var description: String { return name }
    init(dictionary: [String: Any] ) {
        self.id = dictionary["city_id"] as? String ?? ""
        self.name = dictionary["city_name"] as? String ?? ""
    }

}

struct Town: CustomStringConvertible {
    let id: String
    let name: String
    // customize the description to your needs
    var description: String { return name }
    init(dictionary: [String: Any]) {
        self.id = dictionary["town_id"] as? String ?? ""
        self.name = dictionary["town_name"] as? String ?? ""
    }
}

从JSON测试初始化​​：

let contact = Contact(json: json)   // crst no call 1

contact               // crst no call 1
contact?.user         // name: crst - email: crat@gmail.com - phone: 018833455
contact?.user.name    //  "crst"
contact?.user.email   //  "crat@gmail.com"
contact?.user.phone   //  "018833455"
contact?.address      //  100, B, Galway city center,Galway
contact?.address.id           //  200
contact?.address.street       //  B
contact?.address.town         // Galway city center
contact?.address.city         //  Galway
contact?.deliveryInstruction  // "no call"
contact?.deliveryMethod       //    1