如何在Swift中提供具有错误类型的本地化描述？

Question

我正在使用Swift 3语法定义自定义错误类型,我想提供一个用户友好的错误描述,该描述由对象的localizedDescription属性返回Error.我该怎么做？

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.)"

有没有办法让localizedDescription我返回我的自定义错误描述("用户友好的错误描述.")？请注意,此处的错误对象是类型Error而不是MyError.当然,我可以将对象强制转换为MyError

(error as? MyError)?.localizedDescription

但是有没有办法让它工作而不会转换为我的错误类型？

Answer 1

如Xcode 8 beta 6发行说明中所述,

Swift定义的错误类型可以通过采用新的LocalizedError协议提供本地化的错误描述.

在你的情况下:

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.

如果错误转换为NSError(始终可以),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.")

通过采用该CustomNSError协议,错误可以提供userInfo字典(以及a domain和code).例:

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

我还要补充一下,如果你的错误有这样的参数

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

您可以在本地化描述中调用这些参数,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"
  }
}

你甚至可以这样缩短:

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

这对我有用：

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

Answer 4

现在，您的错误类型可以采用两种错误采用协议，以便为 Objective-C 提供附加信息——LocalizedError 和 CustomNSError。这是一个同时采用它们的示例错误：

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" }

}