在 IOS 中解析 Json 响应时出现 valueNotFound 错误答案

【问题标题】：valueNotFound error while parsing Json response in IOS在 IOS 中解析 Json 响应时出现 valueNotFound 错误
【发布时间】：2019-05-01 07:49:43
【问题描述】：

我正在尝试使用 JSONDecoder 解析响应。如果对应的key有value则编译成功，但是如果key有null值则编译失败，报如下错误。

valueNotFound(Swift.String, Swift.DecodingError.Context(codingPath: [编码键（字符串值：“结果”，intValue：无）， _JSONKey(stringValue: "Index 0", intValue: 0), CodingKeys(stringValue: "VehicleName", intValue: nil)], debugDescription: "预期的字符串值，但找到了 null。”，基础错误：nil))

guard let obj = try? JSONDecoder().decode(ShipmentsResponse.self, from: json) else {return}

这是我拒绝的 Shipment 类

class ShipmentResponse : Codable {

    var ItemId: String = ""
    var VehicleName: String  = ""
    var VehicleNumber: String  = ""

    convenience required init(from decoder: Decoder) throws
    {
        self.init()
        let values = try decoder.container(keyedBy: CodingKeys.self)
        ItemId = try values.decode(String.self, forKey: .ItemId)

        do {
            _ = try values.decode(String.self, forKey: .VehicleName)
        } catch {
            print(error)
        }

        VehicleName = try values.decode(String.self, forKey: .VehicleName)
        VehicleNumber = try values.decode(String.self, forKey: .VehicleNumber)
    }

}

这是json

{
    "ItemId": "8af66c87-9099-42a7-8a34-39def02160ac",
    "VehicleName": null,
    "VehicleNumber": null
}

【问题讨论】：

标签： ios json swift parsing jsondecoder

【解决方案1】：

错误很明显。

预期的字符串值，但发现为空

预期值是字符串，但我们在响应中得到null。因此，如果解码器要将null 值解码为非可选类型，则会引发错误。因此，通过在参数中设置空字符串来处理它。

型号代码：

class ShipmentResponse : Codable {

    var itemId: String
    var vehicleName: String
    var vehicleNumber: String

    enum CodingKeys: String, CodingKey {
        case itemId = "ItemId"
        case vehicleName = "VehicleName"
        case vehicleNumber = "VehicleNumber"
    }

    required init(from decoder: Decoder) throws {

        let container = try decoder.container(keyedBy: CodingKeys.self)
        self.itemId = try container.decodeIfPresent(String.self, forKey: .itemId) ?? ""
        self.vehicleName = try container.decodeIfPresent(String.self, forKey: .vehicleName) ?? ""
        self.vehicleNumber = try container.decodeIfPresent(String.self, forKey: .vehicleNumber) ?? ""
    }

    func encode(to encoder: Encoder) throws {

        var container = encoder.container(keyedBy: CodingKeys.self)
        try container.encode(itemId, forKey: .itemId)
        try container.encode(vehicleName, forKey: .vehicleName)
        try container.encode(vehicleNumber, forKey: .vehicleNumber)
    }
}

JSON 解析：

let data = """
{
    "ItemId": "8af66c87-9099-42a7-8a34-39def02160ac",
    "VehicleName": null,
    "VehicleNumber": null
}
""".data(using: String.Encoding.utf8)!

do {
    let jsonData = try JSONDecoder().decode(ShipmentResponse.self, from: data)
    print("\(jsonData.itemId) \(jsonData.vehicleNumber)")
} catch let error {
    print(error)
}

【讨论】：