如果密钥不存在，则解码失败答案

【问题标题】：Decoding fails if keys not present如果密钥不存在，则解码失败
【发布时间】：2021-11-16 16:55:19
【问题描述】：

如果密钥不存在，则解码失败。如果还缺少密钥，如何安全解码。

我已经使用了 Optional 或 Nil 值，但仍然无法解码对象。

低于我的 Json

{
   "mandatory":true,
   "dynamic_obj":[
      {
         "dt":"2021-09-22 01:29:52",
         "url":"https://res._22_01_29.pdf",
         "desc":"PAN CARD",
         "flag":1,
         "count":"2",
         "field":"pan_card",
         "address":"300-435, Nattu Muthu St, Sheethammal Colony, Venus Colony, Chennai, Tamil Nadu 600018, India",
         "visible":true,
         "latitude":13.0389309,
         "longitude":80.2473746
      },
      {
         "url":"https://res.cloudin/no-image.jpg",
         "desc":"driving License",
         "count":"2",
         "field":"driving_license",
         "visible":true
      }
   ]
}

模型类在下面

struct Dynamic_obj : Codable {
    var dt : String?
    var url : String?
    let desc : String?
    var flag : Int?
    let count : String?
    let field : String?
    let visible : Bool?
    
    var bankname : String = "NA"
    var pdfPassword : String = "NA"
    var latitude : String = "NA"
    var longitude : String = "NA"
    var address : String = "NA"

    enum CodingKeys: String, CodingKey {

        case dt = "dt"
        case url = "url"
        case desc = "desc"
        case flag = "flag"
        case count = "count"
        case field = "field"
        case visible = "visible"
        
        case bankname = "bankname"
        case pdfPassword = "pdfPassword"
        case latitude = "latitude"
        case longitude = "longitude"
        case address = "address"
    }

    init(from decoder: Decoder) throws {
        let values = try decoder.container(keyedBy: CodingKeys.self)
        dt = try values.decodeIfPresent(String.self, forKey: .dt)
        url = try values.decodeIfPresent(String.self, forKey: .url)
        desc = try values.decodeIfPresent(String.self, forKey: .desc)
        flag = try values.decodeIfPresent(Int.self, forKey: .flag)
        count = try values.decodeIfPresent(String.self, forKey: .count)
        field = try values.decodeIfPresent(String.self, forKey: .field)
        visible = try values.decodeIfPresent(Bool.self, forKey: .visible)
        
        bankname = try values.decodeIfPresent(String.self, forKey: .bankname) ?? "NA"
        pdfPassword = try values.decodeIfPresent(String.self, forKey: .pdfPassword) ?? "NA"
        latitude = try values.decodeIfPresent(String.self, forKey: .latitude) ?? "NA"
        longitude = try values.decodeIfPresent(String.self, forKey: .longitude) ?? "NA"
        address = try values.decodeIfPresent(String.self, forKey: .address) ?? "NA"
    }

}


                            let decoder = JSONDecoder()
                            do {
                                let responseModel = try decoder.decode(LoanDocxPending.self, from: data)
                                if let mandotory = responseModel.mandatory{
                                    self.visibleDocuments["Identity Proof-~id_proof"] = idProof
                                    self.visibleTitle.append("Identity Proof")
                                }
                            } catch {
                                print("error")
                                
                            }

struct LoanDocxPending :Codable {
    let mandatory : Bool?
    var dynamic_obj : [Dynamic_obj]?

    enum CodingKeys: String, CodingKey {

        case mandatory = "mandatory"
        case dynamic_obj = "dynamic_obj"
    }

    init(from decoder: Decoder) throws {
        let values = try decoder.container(keyedBy: CodingKeys.self)
        mandatory = try values.decodeIfPresent(Bool.self, forKey: .mandatory)
        dynamic_obj = try values.decodeIfPresent([Dynamic_obj].self, forKey: .dynamic_obj)
    }

}

【问题讨论】：

无关但catch { print("error") } 几乎没用。取而代之的是print("error: \(error)")！然后，阅读错误...然后您会看到它以latitude 失败，因为您需要一个字符串，但它是一个双精度...与经度相同，然后它应该可以工作...如果缺少密钥，确实应该是decodeIfPresent()...
非常感谢@Larme careless my side

标签： ios json swift decode

【解决方案1】：

首先，您的大部分代码都不需要，例如 init 方法和几乎所有 CodingKeys。

第二个是在 cmets 中提到的，而不是打印无意义的文字“错误”，而是打印 error 实例。它会告诉你latitude 和longitude 是Double，而不是String。

此模型与问题中的 JSON 匹配

struct DynamicObj : Codable {
    let dt : String?
    let url, desc : String
    let flag : Int?
    let count, field : String
    let visible : Bool
    
    var bankname, pdfPassword, address : String?
    var latitude, longitude : Double?
}

struct LoanDocxPending :Codable {
    let mandatory : Bool
    var dynamicObj : [DynamicObj]

    enum CodingKeys: String, CodingKey {
        case mandatory,dynamicObj = "dynamic_obj"
    }
}

let decoder = JSONDecoder()
do {
    let responseModel = try decoder.decode(LoanDocxPending.self, from: data)
    print(responseModel.mandatory)
} catch {
    print("error", error)
    
}

【讨论】：