依赖链的API调用

Question

我正在尝试链接两个API请求。一种用于生成新令牌，另一种用于获取元素列表（一个需要有效令牌）。

这些方法的调用看起来像这样：

    AuthService.shared().authenticate() { result in
        DispatchQueue.main.async {
            switch result {
               case .failure (let error):
                    // error processing
                    self.alertError(errorTitle: "", errorText: NSLocalizedString("Error generating token", comment: "Signup"))
               case .success (let result):
                    self.alertError(errorTitle: "", errorText: NSLocalizedString("Token collected \(result)", comment: "Signup"))
            }
        }
    }

    ListService.shared().listAll() { result in
        DispatchQueue.main.async {
            switch result {
               case .failure (let error):
                    // error processing
                    self.alertError(errorTitle: "", errorText: NSLocalizedString("Error fetching list", comment: "List"))
               case .success (let result):
                    self.alertError(errorTitle: "", errorText: NSLocalizedString("List fetched \(result)", comment: "List"))
            }
        }
    }

我想做的是尝试调用ListService.shared().listAll()，如果失败并出现错误，我想调用AuthService.shared().authenticate()，然后再次调用ListService.shared().listAll()。

您认为这是个好方法吗？

Answer 1

您可能会发现值得探究PromiseKit，如果不是现在，那么最终（https://github.com/mxcl/PromiseKit）。然后，您可以使用它来执行以下操作：

/**
This is just a facer for the real list all.
It will do the list all request, doing the authentication if it needs too.
*/
func listAll() {

    firstly {
        // Do the real list all
    }.recover {
        // List all failed, so we will attempt to recover

        firstly {
            // Do the authenticate
        }.then {
            // Authenticate succeeded. Do the real list all
        }
    }.done {
        // List all succeeded
    }.catch {
        // List all failed, and we tried to recover,
        // but a part of that also failed
    }
}

Answer 2

1. 混乱的方式-只需按照您指定的顺序将所有3个呼叫嵌套在一起：

   ListService.shared().listAll() { result in
       DispatchQueue.main.async {
           switch result {
           case .failure (let error):
               // error processing
               self.alertError(errorTitle: "", errorText: NSLocalizedString("Error fetching list", comment: "List"))
   
               AuthService.shared().authenticate() { result in
                   DispatchQueue.main.async {
                       switch result {
                       case .failure (let error):
                           // error processing
                           self.alertError(errorTitle: "", errorText: NSLocalizedString("Error generating token", comment: "Signup"))
                       case .success (let result):
                           self.alertError(errorTitle: "", errorText: NSLocalizedString("Token collected \(result)", comment: "Signup"))
   
                           ListService.shared().listAll() { result in
                               DispatchQueue.main.async {
                                   switch result {
                                   case .failure (let error):
                                       // error processing
                                       self.alertError(errorTitle: "", errorText: NSLocalizedString("Error fetching list", comment: "List"))
                                   case .success (let result):
                                       self.alertError(errorTitle: "", errorText: NSLocalizedString("List fetched \(result)", comment: "List"))
                                   }
                               }
                           }
                       }
                   }
               }
   
           case .success (let result):
               self.alertError(errorTitle: "", errorText: NSLocalizedString("List fetched \(result)", comment: "List"))
           }
       }
   }
   

2. 总是尝试先进行身份验证-这可能会导致不必要的身份验证调用，但可以避免嵌套太多代码，并且比第一次失败的listAll(）方法的最坏情况还好，总共3个API调用（再次为listAll()，authenticate()，listAll()）

   AuthService.shared().authenticate() { result in
       DispatchQueue.main.async {
           switch result {
           case .failure (let error):
               // error processing
               self.alertError(errorTitle: "", errorText: NSLocalizedString("Error generating token", comment: "Signup"))
           case .success (let result):
               self.alertError(errorTitle: "", errorText: NSLocalizedString("Token collected \(result)", comment: "Signup"))
   
               ListService.shared().listAll() { result in
                   DispatchQueue.main.async {
                       switch result {
                       case .failure (let error):
                           // error processing
                           self.alertError(errorTitle: "", errorText: NSLocalizedString("Error fetching list", comment: "List"))
                       case .success (let result):
                           self.alertError(errorTitle: "", errorText: NSLocalizedString("List fetched \(result)", comment: "List"))
                       }
                   }
               }
           }
       }
   }
   

3. 更新您的authenticate()方法以将令牌存储在本地，并在访问API之前检查其是否存在。然后更新您的listAll()方法以始终先调用authenticate()。假设您的令牌可用于多个API调用，两次调用之间不会过期，等等：

    class AuthService {
        private var token: String?

        static func shared() -> AuthService {
            return AuthService()
        }

        func authenticate(completion: @escaping (Result<String, Error>) -> Void) {
            if let token = token { 
                completion(.success(token))
                return
            }

            // Make your API call here and store the token when it completes
        }
    }

    class ListService {
        static func shared() -> ListService {
            return ListService()
        }

        func listAll(completion: @escaping (Result<Any, Error>) -> Void) {
            AuthService.shared().authenticate() { authResult in
                switch authResult {
                    case .failure (let error):
                        completion(.failure(error))
                    case .success (let token): 
                    // Make your list API call here
                }
            }
        }
    }

现在您可以像往常一样调用listAll()方法，它将始终通过身份验证：

    ListService.shared().listAll() { result in
        DispatchQueue.main.async {
            switch result {
            case .failure (let error):
                // error processing
                self.alertError(errorTitle: "", errorText: NSLocalizedString("Error fetching list", comment: "List"))
            case .success (let result):
                self.alertError(errorTitle: "", errorText: NSLocalizedString("List fetched \(result)", comment: "List"))
            }
        }
    }