Error協(xié)議是用來進行錯誤處理的。
源碼如下：
public protocol Error {
}
extension Error {
//錯誤的本地化描述
public var localizedDescription: String { get }
}
extension Error where Self.RawValue : SignedInteger {
}
extension Error where Self.RawValue : UnsignedInteger {
}
可以看到，標準庫中只提供了一個localizedDescription只讀屬性呕屎，用來描述錯誤的具體信息磺陡。除此之外趴梢，并沒有其他的方法。
Apple官方推薦使用枚舉類型币他，具體說明如下坞靶。
Swift's enumerations are well suited to represent simple errors. Create an enumeration that conforms to the Error protocol with a case for each possible error. If there are additional details about the error that could be helpful for recovery, use associated values to include that information.
關(guān)于錯誤處理，我自己對這方面的了解的也不夠深蝴悉。這里我給大家介紹一下Alamofire的AFError類彰阴，間接的來了解一下Error協(xié)議的用法。
定義
public enum AFError: Error {
public enum ParameterEncodingFailureReason {
case missingURL
case jsonEncodingFailed(error: Error)
case propertyListEncodingFailed(error: Error)
}
public enum MultipartEncodingFailureReason {
case bodyPartURLInvalid(url: URL)
case bodyPartFilenameInvalid(in: URL)
case bodyPartFileNotReachable(at: URL)
. . .
}
public enum ResponseValidationFailureReason {
case dataFileNil
case dataFileReadFailed(at: URL)
case missingContentType(acceptableContentTypes: [String])
. . .
}
public enum ResponseSerializationFailureReason {
case inputDataNil
case inputDataNilOrZeroLength
case inputFileNil
. . .
}
case invalidURL(url: URLConvertible)
case parameterEncodingFailed(reason: ParameterEncodingFailureReason)
case multipartEncodingFailed(reason: MultipartEncodingFailureReason)
case responseValidationFailed(reason: ResponseValidationFailureReason)
case responseSerializationFailed(reason: ResponseSerializationFailureReason)
}
每個case分別對應(yīng)一種錯誤類型拍冠，并關(guān)聯(lián)一個Reason尿这。
嵌套4個Reason枚舉簇抵，來對錯誤的原因再次進行分類。不得不說代碼很有邏輯感射众，也寫的很好看碟摆。
錯誤描述
extension AFError.ParameterEncodingFailureReason {
var localizedDescription: String {
switch self {
case .missingURL:
return "URL request to encode was missing a URL"
case .jsonEncodingFailed(let error):
return "JSON could not be encoded because of error:\n\(error.localizedDescription)"
case .propertyListEncodingFailed(let error):
return "PropertyList could not be encoded because of error:\n\(error.localizedDescription)"
}
}
}
extension AFError.MultipartEncodingFailureReason {
var localizedDescription: String {
switch self {
case .bodyPartURLInvalid(let url):
return "The URL provided is not a file URL: \(url)"
case .bodyPartFilenameInvalid(let url):
return "The URL provided does not have a valid filename: \(url)"
case .bodyPartFileNotReachable(let url):
return "The URL provided is not reachable: \(url)"
. . .
}
}
}
extension AFError.ResponseSerializationFailureReason {
var localizedDescription: String {
switch self {
case .inputDataNil:
return "Response could not be serialized, input data was nil."
case .inputDataNilOrZeroLength:
return "Response could not be serialized, input data was nil or zero length."
case .inputFileNil:
return "Response could not be serialized, input file was nil."
. . .
}
}
}
extension AFError.ResponseValidationFailureReason {
var localizedDescription: String {
switch self {
case .dataFileNil:
return "Response could not be validated, data file was nil."
case .dataFileReadFailed(let url):
return "Response could not be validated, data file could not be read: \(url)."
case .missingContentType(let types):
return (
"Response Content-Type was missing and acceptable content types " +
"(\(types.joined(separator: ","))) do not match \"*/*\"."
)
. . .
}
}
}
使用localizedDescription屬性，對每一個Reason的分支叨橱，進行詳細的描述典蜕。
當然了，AFError并不是只有這些內(nèi)容罗洗，還有很多方便我們使用的擴展等愉舔，由于它并不是我這篇文章的主要討論方向，就不做更多介紹了栖博。 有興趣的可以去看看下面這個參考鏈接屑宠。
http://www.reibang.com/p/99e6ba32f244
