Coding Error

This is the struct...


struct Blueline: Decodable {
    let ctatt: Ctatt?
}

struct Ctatt: Decodable {
    let tmst: String?
    let errCD: String?
    let errNum: String?
    let eta: [eta?]

    enum CodingKeys: String, CodingKey {
        case tmst
        case errCD = "errCd"
        case errNum
        case eta
    }

    init(from decoder: Decoder) throws {
        let container = try decoder.container(keyedBy: CodingKeys.self)
  
        self.tmst = try container.decode(String.self, forKey: .tmst)
        self.errCD = try container.decode(String.self, forKey: .errCD)
        self.errNum = try container.decodeIfPresent(String.self, forKey: .errNum)
        self.eta = try container.decode(Array.self, forKey: .eta)
    }
}

struct eta: Decodable {
    let staNm: String?
    let stpDe: String?
    let rn: String?
    let rt: String?
    let destSt: String?
    let destNm: String?
    let prdt: String?
    let arrT: String?
    let lat: String?
    let lon: String?

    enum CodingKeys: String, CodingKey {
        case staNm
        case stpDe
        case rn
        case rt
        case destSt
        case destNm
        case prdt
        case arrT
        case lat
        case lon
    }
    
    init(from decoder: Decoder) throws {
        let container = try decoder.container(keyedBy: CodingKeys.self)

        self.staNm = try container.decode(String.self, forKey: .staNm)
        self.stpDe = try container.decode(String.self, forKey: .stpDe)
        self.rn = try container.decode(String.self, forKey: .rn)
        self.rt = try container.decode(String.self, forKey: .rt)
        self.destSt = try container.decode(String.self, forKey: .destSt)
        self.destNm = try container.decode(String.self, forKey: .destNm)
        self.prdt = try container.decode(String.self, forKey: .prdt)
        self.arrT = try container.decode(String.self, forKey: .arrT)
        self.lat = try container.decode(String.self, forKey: .lat)
        self.lon = try container.decode(String.self, forKey: .lon)
    }
}

This is the error...

API status: 200
valueNotFound(Swift.String, Swift.DecodingError.Context(codingPath: [CodingKeys(stringValue: "ctatt", intValue: nil), CodingKeys(stringValue: "eta", intValue: nil), _JSONKey(stringValue: "Index 1", intValue: 1), CodingKeys(stringValue: "lat", intValue: nil)], debugDescription: "Expected String value but found null instead.", underlyingError: nil))

Take a careful look at the error. Specifically, this:

Code Block  
codingPath: [
    CodingKeys(stringValue: "ctatt", intValue: nil),
    CodingKeys(stringValue: "eta", intValue: nil),
    _JSONKey(stringValue: "Index 1", intValue: 1),
    CodingKeys(stringValue: "lat", intValue: nil)
]

gives you the path to the problem, namely ctatt \> eta \> \[1\] \> lat. And this:

Code Block  
"Expected String value but found null instead."

tells you what went wrong. Now look at the code at the end of that path:

Code Block  
self.lat = try container.decode(String.self, forKey: .lat)

The .decode(_:forKey:) method throws if the property is missing. You want the .decodeIfPresent(_:forKey:) variant.

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Quinn “The Eskimo!” @ Developer Technical Support @ Apple
let myEmail = "eskimo" + "1" + "@apple.com"