如何使用 Alamofire 和 SwiftyJSON 保存来自 Json 的数据？

Question

我正在尝试使用这两个库将 "author" 数据从 json(Link:"https://learnappmaking.com/ex/books.json") 保存到名为 "authors" 的全局变量.但它仅适用于 func Alamofire.request(url).responseJSON 的尾随闭包。当我从除尾随闭包之外的某处访问名为 "authors" 的全局变量时，我得到的是一个空字符串数组。

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

我会尽力回答您的所有问题：

数据持久化
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（保存响应）->self.getAuthors或者getAuthors(same)（在响应 {} 内）

得到结果后，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旋转器来等待网络回答然后你将显示你的下一个控制器

Answer 2

根据直接消息的要求：Swift-only 方法。只需将其粘贴到空白的 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)
  }

}

如何使用 Alamofire 和 SwiftyJSON 保存来自 Json 的数据？

How to save data from Json with Alamofire and SwiftyJSON?

json

ios

swift

alamofire

swifty-json