如何在 Swift 中提供錯誤類型的本地化描述？

Question

我正在使用 Swift 3 語法定義自定義錯誤類型，我想提供一個用戶友好的錯誤描述，該錯誤由Error object 的localizedDescription屬性返回。我該怎么做？

public enum MyError: Error {
  case customError

  var localizedDescription: String {
    switch self {
    case .customError:
      return NSLocalizedString("A user-friendly description of the error.", comment: "My error")
    }
  }
}

let error: Error = MyError.customError
error.localizedDescription
// "The operation couldn’t be completed. (MyError error 0.)"

localizedDescription有沒有辦法返回我的自定義錯誤描述（“用戶友好的錯誤描述。”）？ 請注意，這里的錯誤 object 是Error類型，而不是MyError 。 當然，我可以將 object 轉換為 MyError

(error as? MyError)?.localizedDescription

但是有沒有辦法讓它在不轉換為我的錯誤類型的情況下工作？

Answer 1

如 Xcode 8 beta 6 發行說明中所述，

Swift 定義的錯誤類型可以通過采用新的 LocalizedError 協議來提供本地化的錯誤描述。

在你的情況下：

public enum MyError: Error {
    case customError
}

extension MyError: LocalizedError {
    public var errorDescription: String? {
        switch self {
        case .customError:
            return NSLocalizedString("A user-friendly description of the error.", comment: "My error")
        }
    }
}

let error: Error = MyError.customError
print(error.localizedDescription) // A user-friendly description of the error.

如果錯誤轉換為NSError （這總是可能的），您可以提供更多信息：

extension MyError : LocalizedError {
    public var errorDescription: String? {
        switch self {
        case .customError:
            return NSLocalizedString("I failed.", comment: "")
        }
    }
    public var failureReason: String? {
        switch self {
        case .customError:
            return NSLocalizedString("I don't know why.", comment: "")
        }
    }
    public var recoverySuggestion: String? {
        switch self {
        case .customError:
            return NSLocalizedString("Switch it off and on again.", comment: "")
        }
    }
}

let error = MyError.customError as NSError
print(error.localizedDescription)        // I failed.
print(error.localizedFailureReason)      // Optional("I don\'t know why.")
print(error.localizedRecoverySuggestion) // Optional("Switch it off and on again.")

通過采用CustomNSError協議，錯誤可以提供一個userInfo字典（以及一個domain和code ）。 例子：

extension MyError: CustomNSError {

    public static var errorDomain: String {
        return "myDomain"
    }

    public var errorCode: Int {
        switch self {
        case .customError:
            return 999
        }
    }

    public var errorUserInfo: [String : Any] {
        switch self {
        case .customError:
            return [ "line": 13]
        }
    }
}

let error = MyError.customError as NSError

if let line = error.userInfo["line"] as? Int {
    print("Error in line", line) // Error in line 13
}

print(error.code) // 999
print(error.domain) // myDomain

Answer 2

我還要補充一點，如果你的錯誤有這樣的參數

enum NetworkError: LocalizedError {
  case responseStatusError(status: Int, message: String)
}

您可以在本地化描述中調用這些參數，如下所示：

extension NetworkError {
  public var errorDescription: String? {
    switch self {
    case .responseStatusError(status: let status, message: let message):
      return "Error with status \(status) and message \(message) was thrown"
  }
}

你甚至可以像這樣縮短它：

extension NetworkError {
  public var errorDescription: String? {
    switch self {
    case let .responseStatusError(status, message):
      return "Error with status \(status) and message \(message) was thrown"
  }
}

Answer 3

現在，您的錯誤類型可以采用兩種錯誤采用協議，以便為 Objective-C 提供附加信息——LocalizedError 和 CustomNSError。 這是一個同時采用它們的示例錯誤：

enum MyBetterError : CustomNSError, LocalizedError {
    case oops

    // domain
    static var errorDomain : String { return "MyDomain" }
    // code
    var errorCode : Int { return -666 }
    // userInfo
    var errorUserInfo: [String : Any] { return ["Hey":"Ho"] };

    // localizedDescription
    var errorDescription: String? { return "This sucks" }
    // localizedFailureReason
    var failureReason: String? { return "Because it sucks" }
    // localizedRecoverySuggestion
    var recoverySuggestion: String? { return "Give up" }

}

Answer 4

使用結構可以是一種替代方法。 靜態本地化的優雅：

import Foundation

struct MyError: LocalizedError, Equatable {

   private var description: String!

   init(description: String) {
       self.description = description
   }

   var errorDescription: String? {
       return description
   }

   public static func ==(lhs: MyError, rhs: MyError) -> Bool {
       return lhs.description == rhs.description
   }
}

extension MyError {

   static let noConnection = MyError(description: NSLocalizedString("No internet connection",comment: ""))
   static let requestFailed = MyError(description: NSLocalizedString("Request failed",comment: ""))
}

func throwNoConnectionError() throws {
   throw MyError.noConnection
}

do {
   try throwNoConnectionError()
}
catch let myError as MyError {
   switch myError {
   case .noConnection:
       print("noConnection: \(myError.localizedDescription)")
   case .requestFailed:
       print("requestFailed: \(myError.localizedDescription)")
   default:
      print("default: \(myError.localizedDescription)")
   }
}

Answer 5

這個對我有用：

NSError(domain: "com.your", code: 0, userInfo: [NSLocalizedDescriptionKey: "Error description"])

Answer 6

這是更優雅的解決方案：

  enum ApiError: String, LocalizedError {

    case invalidCredentials = "Invalid credentials"
    case noConnection = "No connection"

    var localizedDescription: String { return NSLocalizedString(self.rawValue, comment: "") }

  }

Answer 7

 enum NetworkError: LocalizedError { case noConnection public var description: String { ///You can switch self here if you have multiple cases. return "No inte.net connection" } // You need to implement `errorDescription`, not `localizedDescription`. public var errorDescription: String? { return description } }