Swift 使用Codable協(xié)議進(jìn)行json轉(zhuǎn)模型

1.序列化和反序列化

  • 序列化：將對(duì)象轉(zhuǎn)換為字節(jié)序列的過(guò)程，在傳遞和保存對(duì)象時(shí)，保證對(duì)象的完整性和完整性，方便在網(wǎng)絡(luò)上傳輸或者保存在文件中
let responseData = try? JSONSerialization.data(withJSONObject: response)
  • 反序列化：將字節(jié)序列恢復(fù)為對(duì)象的過(guò)程，重建對(duì)象，方便使用
let obj = try? JSONSerialization.jsonObject(with: data, options: .allowFragments

2.encode和decode

  • encode：將自身類型編碼成其他外部類型
let data = try? JSONEncoder().encode(obj)
  • decode：將其他外部類型解碼成自身類型
let obj = try? JSONDecoder().decode(T.self, from: data)

3.Codable

public typealias Codable = Decodable & Encodable

實(shí)際上，Codable就是指的編碼和解碼協(xié)議

4.json轉(zhuǎn)模型
4.1在用原生Codable協(xié)議的時(shí)候，需要遵守協(xié)議Codable，結(jié)構(gòu)體，枚舉，類都可以遵守這個(gè)協(xié)議，一般使用struct

struct UserModel:Codable {
    var name:   String?
    var age:    Int?
    var sex:    Bool?
    var name_op: String?
}

注意，你的json里面的字段可能沒有值，因此需要設(shè)置可選值
4.2 json數(shù)據(jù)里面的字段和model字段不一致
解決辦法：實(shí)現(xiàn) enum CodingKeys: String, CodingKey {}這個(gè)映射關(guān)系

struct UserModel:Codable {
    var name:   String?
    var age:    Int?
    var sex:    Bool?
    var name_op: String?
    var nick: String?
    enum CodingKeys: String, CodingKey {
        case name
        case age
        case sex
        case name_op 
        case nick = "nick_name" 
    }
}

上訴代碼中，如果后臺(tái)返回的字段名稱叫做nick_name，但是你想用自己命名的nick，就可以用到上述枚舉中的映射去替換你想要的字段名字。

4.3如果你的模型里面帶有嵌套關(guān)系，比如你的模型里面有個(gè)其他模型或者模型數(shù)組，那么只要保證嵌套的模型里面依然實(shí)現(xiàn)了對(duì)應(yīng)的協(xié)議

struct UserModel:Codable {
    var name:   String?
    var age:    Int?
    var sex:    Bool?
    var name_op: String?
    var nick: String?
    var books_op:   [BookModel]?
    enum CodingKeys: String, CodingKey {
        case name
        case age
        case sex
        case name_op 
        case nick = "nick_name" 
    }
}

// BookModel
struct BookModel:Codable {
    var name:String ?
}

4.4如果json里面數(shù)據(jù)類型和model數(shù)據(jù)類型不一致，最常見的有（Bool和Int，Int和String）這些在后臺(tái)弱類型語(yǔ)言上是不加區(qū)分
解決辦法：定義了一個(gè)可能是Bool或者Int的類型

struct TIntBool:Codable { 
    var int:Int {
        didSet {
            if int == 0 { self.bool = false
            } else { self.bool = true }
        }
    } 
    var bool:Bool {
        didSet {
            if bool { self.int = 1
            } else { self.int = 0 }
        }
    } 
    //自定義解碼(通過(guò)覆蓋默認(rèn)方法實(shí)現(xiàn))
    init(from decoder: Decoder) throws {
        let singleValueContainer = try decoder.singleValueContainer()
        if let intValue = try? singleValueContainer.decode(Int.self) {
            self.int = intValue
            self.bool = (intValue != 0)
        } else if let boolValue = try? singleValueContainer.decode(Bool.self) {
            self.bool = boolValue
            if boolValue { self.int = 1
            } else { self.int = 0 }
        } else {
            self.bool = false
            self.int = 0
        }
    } 
}

下面是一個(gè)Int 或者String類型的

struct TStrInt: Codable {
    var int:Int {
        didSet {
            let stringValue = String(int)
            if  stringValue != string {
                string = stringValue
            }
        }
    } 
    var string:String {
        didSet {
            if let intValue = Int(string), intValue != int {
                int = intValue
            }
        }
    } 
    //自定義解碼(通過(guò)覆蓋默認(rèn)方法實(shí)現(xiàn))
    init(from decoder: Decoder) throws {
        let singleValueContainer = try decoder.singleValueContainer() 
        if let stringValue = try? singleValueContainer.decode(String.self)
        {
            string = stringValue
            int = Int(stringValue) ?? 0
            
        } else if let intValue = try? singleValueContainer.decode(Int.self)
        {
            int = intValue
            string = String(intValue);
        } else
        {
            int = 0
            string = ""
        }
    }
}

因此在模型設(shè)計(jì)的時(shí)候就可以這樣了：

struct UserModel:Codable {
    var name:   String?
    var age:    Int?
    var sex:    Bool?
    var name_op: String?
    var nick: String?
    var books_op:   [BookModel]?
    var stringInt:  TStrInt?
    var boolInt:    TIntBool?
    enum CodingKeys: String, CodingKey {
        case name
        case age
        case sex
        case name_op 
        case nick = "nick_name" 
        case  stringInt
        case boolInt
    }
}

// BookModel
struct BookModel:Codable {
    var name:String ?
}

4.4使用JSONDecoder進(jìn)行json轉(zhuǎn)model

private func jsonToModel<T: Codable>(_ modelType: T.Type, _ response: Any) -> T? {
        guard let data = try? JSONSerialization.data(withJSONObject: response), let info = try? JSONDecoder().decode(T.self, from: data) else {
            return nil
        }
        return info
    }

先使用JSONSerialization進(jìn)行一次序列化操作
看一下decode源碼：

// MARK: - Decoding Values

    /// Decodes a top-level value of the given type from the given JSON representation.
    ///
    /// - parameter type: The type of the value to decode.
    /// - parameter data: The data to decode from.
    /// - returns: A value of the requested type.
    /// - throws: `DecodingError.dataCorrupted` if values requested from the payload are corrupted, or if the given data is not valid JSON.
    /// - throws: An error if any value throws an error during decoding.
    open func decode<T : Decodable>(_ type: T.Type, from data: Data) throws -> T {//泛型并且約束遵守協(xié)議
        let topLevel: Any
        do {
           //反序列化操作
            topLevel = try JSONSerialization.jsonObject(with: data, options: .allowFragments)
        } catch {
            throw DecodingError.dataCorrupted(DecodingError.Context(codingPath: [], debugDescription: "The given data was not valid JSON.", underlyingError: error))
        }
        let decoder = _JSONDecoder(referencing: topLevel, options: self.options)
        
        //調(diào)用unbox解碼并返回解碼后的數(shù)據(jù)
        guard let value = try decoder.unbox(topLevel, as: type) else {
            throw DecodingError.valueNotFound(type, DecodingError.Context(codingPath: [], debugDescription: "The given data did not contain a top-level value."))
        }

        return value
    }

可以看到在轉(zhuǎn)model的時(shí)候，先進(jìn)行一次序列化操作，decode內(nèi)部又進(jìn)行一次反序列化操作，蘋果這樣設(shè)計(jì)估計(jì)是在參數(shù)傳遞的時(shí)候想讓我們傳遞字節(jié)流

至此就可以使用swift原生協(xié)議Codable進(jìn)行json轉(zhuǎn)model了

JSON字符串轉(zhuǎn)模型

這是一個(gè)字符串

let jsonString:String = """
           {
             "name":"Tomas",
             "age":"10",
             "gender":"man"
        
           }
        """

如果將它解析成User對(duì)象

let jsonData: Data = jsonString.data(using:String.Encoding.utf8)!
let decoder = JSONDecoder()
 do {
      let user:UserModel = try decoder.decode(UserModel.self,from:jsonData)
    } catch {

}
JSONSerialization

Serialization 是序列化的意思，JSONSerialization 顧名思義是對(duì)JSON進(jìn)行序列化。

JSONSerialization 是對(duì) JSON 字符串進(jìn)行序列化和反序列化的工具類。用這個(gè)類可以將JSON轉(zhuǎn)成對(duì)象，也可以將對(duì)象轉(zhuǎn)成JSON。

let dict:[String:Any] = ["name":"jack",
                          "age":10,
                       "gender":"man"]
if JSONSerialization.isValidJSONObject(dict) == false {
            return
        }
        
let data:Data = try! JSONSerialization.data(withJSONObject: dict, options: .fragmentsAllowed);
 // 將data轉(zhuǎn)換成制定model
guard let Model:UserModel = try? JSONDecoder().decode(UserModel.self, from: data) else {
            return
        }
        // 將data轉(zhuǎn)成字符串輸出
let string = String(data: data, encoding: String.Encoding.utf8)
print(string)
print(Model.name)

Optional("{\"name\":\"jack\",\"gender\":\"man\",\"age\":10}")
Optional("jack")
  • JSON轉(zhuǎn)字典
let jsonString = "{\"name\":\"jack\",\"age\":10}";
let data = jsonString.data(using: .utf8)
let dict = try! JSONSerialization.jsonObject(with: data!, options: .allowFragments)
        print(dict)
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