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swift - 实例成员不能用于可编码 JSON 类型

问题描述

除了 JSONDecoder 块之外，我似乎无法在任何地方访问结构成员。如何在其他地方访问这些 api 返回值，例如在可以在任何地方调用并返回 api 数据的函数中。最后一行超出范围或不允许。

class ViewController: UIViewController {


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

    override func viewDidAppear(_ animated: Bool) {
        super.viewDidAppear(animated)

        struct ObjectLookup: Codable {
            let ObjectID: Int?
            let ObjectName: String?
            let Creators: String?
            let Medium: String?
            let Titles: String?
            let LabelUUID: String?

            static func fetch(withID id : String){
                let urlString = DomainURL + "\(id)"



                print("urlString is \(urlString)" )
                if let url = URL(string: urlString) {
                    let task = URLSession.shared.dataTask(with: url, completionHandler: { (data,response,error) in
                        print(String(data: data!,encoding: .ascii) ?? "no data")

                        if let ObjectLookup = try? JSONDecoder().decode(ObjectLookup.self, from: data!) {
                            print( ObjectLookup.ObjectName ?? "no url")

                        }

                    })
                    task.resume()

                }else{
                    print("bad url")
                }
            }
        }




        ObjectLookup.fetch(withID: "2322A63C74C92")
        let myName = ObjectLookup.ObjectName

    }

标签： swiftapidecodable

解决方案

将其重构为

class ViewController: UIViewController {


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

        ObjectLookup.fetch(withID: "2322A63C74C92") { obj in
          print(obj?.ObjectName)
        }

    }

    override func viewDidAppear(_ animated: Bool) {
        super.viewDidAppear(animated)


    }

}

struct ObjectLookup: Codable {
    let ObjectID: Int?
    let ObjectName: String?
    let Creators: String?
    let Medium: String?
    let Titles: String?
    let LabelUUID: String?

    static func fetch(withID id : String,completion:@escaping(_ ret:ObjectLookup?) -> Void ){
        let urlString = DomainURL + "\(id)" 

        print("urlString is \(urlString)" )
        if let url = URL(string: urlString) {
            let task = URLSession.shared.dataTask(with: url, completionHandler: { (data,response,error) in
                print(String(data: data!,encoding: .ascii) ?? "no data")

                if error != nil {
                  compeltion(nil)
                  return
                }

                if let res = try? JSONDecoder().decode(ObjectLookup.self, from: data!) {
                    print( res.ObjectName ?? "no url")
                    completion(res)

                }

            })
            task.resume()

        }else{
            print("bad url")
            completion(nil)
        }
    }
}

不要大写变量名的第一个字母使用camelCase（只对类这样做），我知道更改任何字母都会破坏编码过程，所以请记住它或使用CodingKeys来转换变量，还要注意URLSession.shared.dataTask回调在后台队列中，所以考虑使用

DispatchQueue.main.async {}

viewDidLoad如果你想做任何 UI 操作，内部回调

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