在iOS中解析Json响应时出现valueNotFound错误

Question

我正在尝试使用解析响应JSONDecoder。如果相应的键有值，那么它将很好，但是如果键的值为空，则它将无法编译，并出现以下错误。

valueNotFound（Swift.String，Swift.DecodingError.Context（codingPath：[CodingKeys（stringValue：“ Results”，intValue：nil），_JSONKey（stringValue：“ Index 0”，intValue：0），CodingKeys（stringValue：“ VehicleName”， intValue：nil）]，debugDescription：“期望的字符串值，但发现为null。”，底层错误：nil））

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

这是我违抗的货运类

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
}

Answer 1

错误很明显。

预期的字符串值，但发现为 null

预期值是字符串，但我们正在收到null响应。因此，如果解码器要将null值解码为非可选类型，则会抛出错误。因此，通过在参数中创建空字符串来处理它。

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)
}