valueNotFound error while parsing Json response in IOS

Question

I am trying to parse a response using the JSONDecoder. If there is value for the corresponding key then it goes well, but if there is null value for a key then it fails to compile with the following error.

valueNotFound(Swift.String, Swift.DecodingError.Context(codingPath: [CodingKeys(stringValue: "Results", intValue: nil), _JSONKey(stringValue: "Index 0", intValue: 0), CodingKeys(stringValue: "VehicleName", intValue: nil)], debugDescription: "Expected String value but found null instead.", underlyingError: nil))

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

here is the Shipment class that i defied

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)
    }

}

Here is the json

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

Answer 1

The error is very clear that.

Expected String value but found null instead

Expected value is string but we are getting null in the response. So the decoder throws an error if it's going to decode a null value to a non-optional type. So, handle it by making the empty string in the parameters.

Model code:

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 parsing:

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)
}