我正在使用 Swift 3 语法定义自定义错误类型,并且我想提供由 Error
的 localizedDescription
属性返回的错误的用户友好描述> 对象。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
返回我的自定义错误描述(“用户友好的错误描述。”)?请注意,这里的错误对象是 Error
类型,而不是 MyError
类型。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转换为我的错误类型?
最佳答案
如 Xcode 8 beta 6 发行说明中所述,
Swift-defined error types can provide localized error descriptions by adopting the new LocalizedError protocol.
就您而言:
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.
如果错误已转换,您可以提供更多信息
到 NSError
(这总是可能的):
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CustomNSError
协议(protocol),错误可以提供
一个userInfo
字典(还有一个domain
和code
)。示例:
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
关于swift - 如何在 Swift 中提供带有错误类型的本地化描述?,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/40590252/