Swift如何解码OpenSky API返回的无键JSON数组为Codable自定义模型

报错原因 #

Swift 默认的 Codable 自动合成逻辑会期望 StateVector 对应的 JSON 结构是键值对字典，但 OpenSky 返回的 states 数组下每个元素都是按固定顺序排布的无键数组，因此需要手动实现 StateVector 的解码逻辑，按索引读取数组元素赋值给对应属性。

另外原代码存在两处类型不匹配问题需要修正：

• icao24 是6位十六进制字符串，并非 UUID 类型，需改为 String
• API 部分字段可能返回 null，对应属性需要声明为可选类型

修正后的完整代码 #

首先修改 StateVector 结构体，添加手动解码实现：

struct FlightState: Codable {
    let time: Int
    let states: [StateVector]

    struct StateVector: Codable {
        let icao24: String
        let callsign: String?
        let origin_country: String
        let time_position: Int?
        let last_contact: Int
        let longitude: Float?
        let latitude: Float?
        let baro_altitude: Float?
        let on_ground: Bool
        let velocity: Float?
        let true_track: Float?
        let vertical_rate: Float?
        let sensors: [Int]?
        let geo_altitude: Float?
        let squawk: String?
        let spi: Bool
        let position_source: Int
        
        init(from decoder: Decoder) throws {
            // 解码为无键数组容器，按顺序读取元素
            var container = try decoder.unkeyedContainer()
            icao24 = try container.decode(String.self)
            // 呼号默认带尾部空格，这里加了trim处理，不需要可删除
            callsign = try container.decodeIfPresent(String.self)?.trimmingCharacters(in: .whitespaces)
            origin_country = try container.decode(String.self)
            time_position = try container.decodeIfPresent(Int.self)
            last_contact = try container.decode(Int.self)
            longitude = try container.decodeIfPresent(Float.self)
            latitude = try container.decodeIfPresent(Float.self)
            baro_altitude = try container.decodeIfPresent(Float.self)
            on_ground = try container.decode(Bool.self)
            velocity = try container.decodeIfPresent(Float.self)
            true_track = try container.decodeIfPresent(Float.self)
            vertical_rate = try container.decodeIfPresent(Float.self)
            sensors = try container.decodeIfPresent([Int].self)
            geo_altitude = try container.decodeIfPresent(Float.self)
            squawk = try container.decodeIfPresent(String.self)
            spi = try container.decode(Bool.self)
            position_source = try container.decode(Int.self)
        }
    }
}

原有的解码调用代码不需要修改即可正常运行：

let decoder = JSONDecoder()             
let flightState: FlightState = try! decoder.decode(FlightState.self, from: dataString.data(using: .utf8)!)

内容的提问来源于stack exchange，提问作者elementzero23