Swift Decodable使用样例

1. 使用 Decodable 解析 JSON 样例
2. 具体说明可以看注释

let dateFormatter: DateFormatter = {
    let formatter = DateFormatter()
    formatter.dateFormat = "yyyy/MM/dd HH:mm:ss"
    return formatter
}()

// 范型承接**不同类型的**数据
struct Response<T: Decodable>: Decodable, CustomStringConvertible {
    let status: Int
    let message: String?
    let data: T?
    
    // 定义匹配关系 模型键 与 JSON键
    enum CodingKeys: String, CodingKey {
        case status
        case message
        case data
    }

    init(from decoder: Decoder) throws {
        let container = try decoder.container(keyedBy: CodingKeys.self)
        status = try container.decode(Int.self, forKey: .status)
        message = try container.decodeIfPresent(String.self, forKey: .message)
        data = try container.decodeIfPresent(T.self, forKey: .data)
    }

    var description: String {
        return "{status: \(status), message: \(String(describing: message)), data: \(String(describing: data))}"
    }

}

do {
    // 解析 data 为字符串的 数据
    let example1 = """
    {"status":200, "message":null, "data":"is string data"}
    """
    let resp1 = try JSONDecoder().decode(Response<String>.self, from: example1.data(using: .utf8)!)
    print("\(resp1)")

    // 解析 data 为 null 的数据
    let example2 = """
    {"status": 401, "message": "Auth failed", "data": null}
    """
    let resp2 = try JSONDecoder().decode(Response<String>.self, from: example2.data(using: .utf8)!)
    print("\(resp2)")

    // 解析 data 为字符串数组的数据
    let example3 = """
    {
        "status":200,
        "message":null,
        "data": ["A", "B", "C", "D"]
    }
    """
    let resp3 = try JSONDecoder().decode(Response<[String]>.self, from: example3.data(using: .utf8)!)
    print("\(resp3)")

    // 解析自定义类型，其中 score 为 字符串类型 的JSON数据
    let example4 = "{\"status\":200,\"message\":null,\"data\":[{\"name\":\"Eric\",\"tel\":18888888888,\"enrollment_time\":1635136842,\"score\":\"[{\\\"subject\\\":\\\"Math\\\",\\\"score\\\":100},{\\\"subject\\\":\\\"Art\\\",\\\"score\\\":90}]\",\"other\":\"\"},{\"name\":\"Eric\",\"enrollment_time\":1635116842,\"score\":\"\",\"other\":\"\"}]}"

    struct Student: Decodable, CustomStringConvertible {
        let name: String
        let tel: String?
        let enrollmentTime: Date
        let scores: [Score]

        enum CodingKeys: String, CodingKey {
        case name
        case enrollmentTime = "enrollment_time"
        case tel
        case scores = "score"
        }
        
        init(from decoder: Decoder) throws {
            let container = try decoder.container(keyedBy: CodingKeys.self)
            name = try container.decode(String.self, forKey: .name)
            if let temp = try container.decodeIfPresent(Int.self, forKey: .tel) {
                tel = "\(temp)"
            } else {
                tel = nil
            }

            // 日期，手动解析，JSONDecoder 不需要额外配置
            // 也可以通过 decoder.dateDecodingStrategy 设置解析方法
//                let timeInterval = try container.decode(Double.self, forKey: .enrollmentTime)
//                enrollmentTime = Date(timeIntervalSince1970: timeInterval)

            // 日期，自动解析，JSONDecoder 需要配置日期格式
            // decoder.dateDecodingStrategy = .secondsSince1970
            enrollmentTime = try container.decode(Date.self, forKey: .enrollmentTime)
            
            // 手动解析 JSON字符串
            let score = try container.decode(String.self, forKey: .scores)
            if score.count > 0 {
                scores = try JSONDecoder().decode([Score].self, from: score.data(using: .utf8)!)
            } else {
                scores = []
            }
        }

        var description: String {
            let date = dateFormatter.string(from: enrollmentTime)
            return "{name: \(name), tel: \(String(describing: tel)), enrollment_time: \(date), scores: \(scores)}"
        }
    }

    struct Score: Decodable, CustomStringConvertible {
        let subject: String
        let score: Double
        var description: String {
            "{subject: \(subject), score:\(score)}"
        }
    }

    let decoder = JSONDecoder()
    decoder.dateDecodingStrategy = .secondsSince1970
    let resp4 = try decoder.decode(Response<[Student]>.self, from: example4.data(using: .utf8)!)
    print("\(resp4)")
} catch {
    print("\(error)")
}