如何使用 Alamofire 和 SwiftyJSON 从 Json 中保存数据？

Question

我正在尝试使用这两个库从 json(Link:"https://learnappmaking.com/ex/books.json") 将“作者”数据保存到名为“作者”的全局变量中。但它只适用于func Alamofire.request(url).responseJSON 的尾随关闭。当我从尾随闭包之外的某个地方访问名为“authors”的全局变量时，我得到的是一个空的字符串数组。

有人能解释一下这种奇怪情况背后的原因吗？ 非常感谢。

class ViewController: UIViewController {

    var authors = [String]()
    let url = "https://learnappmaking.com/ex/books.json"


    func getAuthorsCount() {
        print("the number of authors : \(authors.count)") // I hope that here, the number of authors should be 3 too! actually, it is 0. Why? 

        // this for loop doesn't get excuted
        for author in authors {
            print(author)
        }
    }

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view.

        Alamofire.request(url).responseJSON { response in
            if let data = response.data {
                if let json = try? JSON(data: data) {
                    for item in json["books"].arrayValue {
                        var outputString: String
                        print(item["author"])
                        outputString = item["author"].stringValue
                        //urlOfProjectAsset.append(outputString)
                        self.authors.append(outputString)
                        print("authors.count: \(self.authors.count)")
                    }
                }
            }
    }

        getAuthorsCount()
        print("-------------")
    }
}

实际输出为：

---

更新： 我调整了我的代码：

class ViewController: UIViewController {

    var authors = [String]()
    let url = "https://learnappmaking.com/ex/books.json"


    func getAuthorsCount() {
        print("the number of authors : \(authors.count)")

        // this for loop doesn't get excuted
        for author in authors {
            print(author)
        }
    }

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view.

        Alamofire.request(url).responseJSON { response in
            if let data = response.data {
                if let json = try? JSON(data: data) {
                    for item in json["books"].arrayValue {
                        var outputString: String
                        //print(item["author"])
                        outputString = item["author"].stringValue
                        //urlOfProjectAsset.append(outputString)
                        self.authors.append(outputString)
                        //print("authors.count: \(self.authors.count)")
                    }
                self.getAuthorsCount() // I added this line of code.
                }
            }
    }
        getAuthorsCount()
        print("-------------")
    }
}

但是为什么func getAuthorsCount()（不是self.version）仍然打印一个空的字符串数组？我认为结果应该与结果相同 func self.getAuthorsCount() 已打印。 我现在很迷茫... 同样，我想使用保存在名为“authors”的变量中的数据，但我只得到一个空字符串数组。

Answer 1

我会尽力回答你所有的问题：

• 数据是持久的

• 您正在执行以下操作：Alamo.request（网络调用）-> getAuthors（打印结果-空）-> response（接收响应）-> self.authors.append（保存响应）-> self.authors（打印结果）

• 你需要做：Alamo.request (网络调用) -> response (接收响应) -> self.authors.append(save response) -> self.getAuthors or getAuthors(same) (在响应内{})

一旦得到结果，您需要在响应回调中调用 getAuthors ：

override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view.

        Alamofire.request(url).responseJSON { response in
            if let data = response.data {
                if let json = try? JSON(data: data) {
                    for item in json["books"].arrayValue {
                        var outputString: String
                        print(item["author"])
                        outputString = item["author"].stringValue
                        //urlOfProjectAsset.append(outputString)
                        self.authors.append(outputString)
                        print("authors.count: \(self.authors.count)")
                    }

                    self.getAuthorsCount()
                    print("-------------")
                   //Do whatever you want from here : present/push 


                }
            }
        }

然后你就可以使用保存的数据了：

• 要将数据发送到另一个 ViewController，您可以使用各种方法（present/push、closure/callback，...）
• 通常你会有一个加载微调器来等待网络 回答然后你会展示你的下一个控制器

Answer 2

根据直接消息的要求：仅 Swift 的方法。只需将其粘贴到空白 Playground 中即可：

import Foundation

final class NetworkService {

  enum ServiceError: LocalizedError {
    case invalidUrl
    case networkingError(error: Error)
    case parsingError

    var localizedDescription: String? { return String(describing: self) }
  }


  func request(completion: @escaping (Result<[UserObject], Error>) -> Void ) {

    guard let url = URL(string: "https://jsonplaceholder.typicode.com/users") else {
      completion(.failure(ServiceError.invalidUrl))
      return
    }

    let dataTask = URLSession.shared.dataTask(with: url) { (jsonData, response, error) in
      if let jsonData = jsonData {
        let jsonDecoder = JSONDecoder()

        do {
          let users = try jsonDecoder.decode([UserObject].self, from: jsonData)
          completion(.success(users))
        } catch {
          completion(.failure(ServiceError.parsingError))
        }

      } else if let error = error {
        completion(.failure(ServiceError.networkingError(error: error)))
      }
    }
    dataTask.resume()

  }
}

struct UserObject: Codable {
  let id: Int
  let name: String
  let username: String
  let email: String?
  let website: String?
}


let networkService = NetworkService()
networkService.request { result in

  switch result {
  case .success(let users):
    debugPrint("Received \(users.count) users from REST API")
    debugPrint(users)
  case .failure(let error):
    debugPrint(error.localizedDescription)
  }

}