Swift - 对“实例成员不能在类型上使用”错误的简单修复？

Question

这是我基于isSteamDown JSON页面做的JSON“解码”/解析：

struct Instruction: Decodable {
    let statuses: [Status]
    let message, messageURL: String
    let status: Bool
    let load, time: Int

    enum CodingKeys: String, CodingKey {
        case statuses, message
        case messageURL = "message_url"
        case status, load, time
    }
}

以下是我编写的用于尝试解码的代码：

class ViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.

        let url = "https://issteamdown.com/status.json"
        let urlObj = URL(string: url)

        URLSession.shared.dataTask(with: urlObj!) {(data, response, error) in

            do {
                guard let json = (try? JSONSerialization.jsonObject(with: data!, options: JSONSerialization.ReadingOptions.mutableContainers)) as? [String: Any] else {
                        return
                    }
                for statusCheck in json {
                    print(Instruction.status)
                }
            } catch {
                print(error)
            }
        }.resume()
    }
}

我遇到的错误是打印线：

for statusCheck in json {
    print(Instruction.status)
}

错误如下：

实例成员“状态”不能用于“指令”类型

我想知道的是：我的代码解决这个特定问题的方法是什么？

另外：是否有一般的解决方案通常适用于此错误格式？

另外，如果问题不是太多，你能不能用尽可能的外行解释你的答案背后的原因？

---

编辑：我尝试将“Instruction.status”更改为“statusCheck.status”并返回错误：

元组类型的值'（键：字符串，值：任意）'没有成员'状态'

Answer 1

状态也应该适应Decodable ..你应该使用如下的JSONDecodable方法。

struct Status: Decodable {
    let title: String
    let code: Int
    let status: Bool
    let time: Int
}

struct Instruction: Decodable {
    let statuses: [Status]
    let message, messageURL: String
    let load: Int

    enum CodingKeys: String, CodingKey {
        case statuses, message
        case messageURL = "message_url"
        case load
    }
}

class ViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.

        let url = "https://issteamdown.com/status.json"
        let urlObj = URL(string: url)

        URLSession.shared.dataTask(with: urlObj!) {(data, response, error) in
            guard let data = data else { return }
            do {
                let json = try JSONDecoder().decode(Instruction.self, from: data)
                json.statuses.forEach { status in
                    print(status)
                }
            } catch {
                print(error)
            }

            }.resume()
    }
}

Answer 2

对于JSONDecoder类型，最好使用JSONSerialization而不是Decodable。

let decoder = JSONDecoder()
guard let instruction = try decoder.decode(Instruction.self, from: data!) else { return }
print(instruction.status) // no need for 'for' loop!

以下是您现有代码的上下文代码：

class ViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.

        let url = "https://issteamdown.com/status.json"
        let urlObj = URL(string: url)

        URLSession.shared.dataTask(with: urlObj!) {(data, response, error) in

            do {
                // write the above code here
            } catch {
                print(error)
            }
        }.resume()
    }
}