[Swift学习笔记] ObjectMapper 框架

Hearst-DD/ObjectMapper

ObjectMapper是用Swift语言实现对象和JSON相互转换的框架

ObjectMapper框架支持的数据结构类型:

• Int
• Bool
• Double
• Float
• String
• RawRepresentable(Enums)
• Array
• Dictionary
• Object
• Array
• Array>
• Set
• Dictionary
• Dictionary>
• Optionals of all the above //上述的可选类型
• Implicitly Unwrapped Optionals of the above //上述的隐式解析可选类型

其中Mappable是ObjectMapper框架中定义的一个接口

public protocol Mappable {
 /// This function can be used to validate JSON prior to mapping.
 /// Return nil to cancel mapping at this point
 init?(_ map: Map)
 /// This function is where all variable mappings should occur. 
 ///It is executed by Mapper during the mapping (serialization and deserialization) process.
 mutating func mapping(map: Map)
}

配置

• 在项目的podfile中添加:

pod 'ObjectMapper', '~> 1.3'

• 运行 pod install

案例

class User: Mappable {
    var username: String?
    var age: Int?
    var weight: Double!
    var array: [AnyObject]?
    var dictionary: [String : AnyObject] = [:]
    var bestFriend: User?                       // Nested User object
    var friends: [User]?                        // Array of Users
    var birthday: NSDate?
    var imageURLs: Array?

    required init?(_ map: Map) {

    }

    // Mappable
    func mapping(map: Map) {
        username    <- map["username"]
        age         <- map["age"]
        weight      <- map["weight"]
        array       <- map["arr"]
        dictionary  <- map["dict"]
        bestFriend  <- map["best_friend"]
        friends     <- map["friends"]
        birthday    <- (map["birthday"], DateTransform())
        posterURL   <- (map["image"], URLTransform())
    }
}

自定义的Model需要实现Mappable接口,并在mapping(map: Map)方法中将Model的属性与JSON结构的Key相映射, 如果ObjectMapper支持该属性的类型的转换, 只需要写

username <- map["username"]

如果ObjectMapper不支持转换就需要调用Mappable额外提供的类, NSDate类型可以用DateTransform()类转换:

birthday <- (map["birthday"], DateTransform())

如果ObjectMapper也没有提供类型转化方法就需要自定义了转换类了, 这里就自定义了一个URLArrayTransform类:

import Foundation
import ObjectMapper

class URLArrayTransform: TransformType {
    typealias Object = Array
    typealias JSON = Array
    
    init() {}
    
    func transformFromJSON(value: AnyObject?) -> Array? {
        if let URLStrings = value as? [String] {
            var listOfUrls = [NSURL]()
            for item in URLStrings {
                if let url = NSURL(string: item) {
                    listOfUrls.append(url)
                }
            }
            return listOfUrls
        }
        return nil
    }
    
    func transformToJSON(value: [NSURL]?) -> JSON? {
        if let urls = value {
            var urlStrings = [String]()
            for url in urls {
                urlStrings.append(url.absoluteString)
            }
            return urlStrings
        }
        
        return nil
    }
}

自定义的转换类需要实现 ObjectMapper 的 TransformType 接口, 从 URLArrayTransform 的实现中可以看出自定义转换类还是比较简单的, 主要就是重写 transformFromJSON 和 transformToJSON 方法.

完整实现了 User 类后, 就可以是 User 和 JSON 字符串相互转换了

let user = User(JSONString: JSONString)

let JSONString = user.toJSONString(prettyPrint: true)  //prettyPrint参数用于生成JSON字符串是否格式化, 以便于打印

使用Mapper类转换
let user = Mapper().map(JSONString: JSONString)

let JSONString = Mapper().toJSONString(user, prettyPrint: true)

补充: AlamofireObjectMapper

tristanhimmelman/AlamofireObjectMapper

该框架可以结合 Alamofire 和 ObjectMapper 使用, 为Alamofire的Request类扩展出了responseObject 和 responseArray 方法, 更方便的将网络通信返回的JSON数据转换成对象

配置

• 在项目的podfile中添加:

pod 'AlamofireObjectMapper', '~> 3.0'

• 运行 pod install

案例

let URL = "..."
Alamofire.request(.GET, URL).responseObject { (response: DataResponse) in

    let weatherResponse = response.result.value

    if let threeDayForecast = weatherResponse?.threeDayForecast {
        for forecast in threeDayForecast {
            print(forecast.day)
            print(forecast.temperature)           
        }
    }
}