ios - 自定义 NSError 代码

Question

我正在构建一个 Cocoa Touch Framework，它使用自定义 NSError 对象将错误反馈给调用者。我需要声明一个定义自定义错误代码的枚举。我去了这个Apple doc其中列出了如下所示的 NSURLErrorDomain 错误代码:

enum {    
   NSURLErrorUnknown = -1,   
   NSURLErrorCancelled = -999,   
   NSURLErrorBadURL = -1000,    
   NSURLErrorTimedOut = -1001,   
   NSURLErrorUnsupportedURL = -1002,
   NSURLErrorUnsupportedURL = -1002,
   NSURLErrorCannotConnectToHost = -1004,   
   NSURLErrorDataLengthExceedsMaximum = -1103,   
   NSURLErrorNetworkConnectionLost = -1005,    
   NSURLErrorDNSLookupFailed = -1006,   
   NSURLErrorHTTPTooManyRedirects = -1007,    
   NSURLErrorResourceUnavailable = -1008,   
   NSURLErrorNotConnectedToInternet = -1009,   
   NSURLErrorRedirectToNonExistentLocation = -1010,   
   NSURLErrorBadServerResponse = -1011,   
   NSURLErrorUserCancelledAuthentication = -1012,   
   NSURLErrorUserAuthenticationRequired = -1013,   
   NSURLErrorZeroByteResource = -1014,   
   NSURLErrorCannotDecodeRawData = -1015,    
   NSURLErrorCannotDecodeContentData = -1016,    
   NSURLErrorCannotParseResponse = -1017,   
   NSURLErrorInternationalRoamingOff = -1018,    
   NSURLErrorCallIsActive = -1019,    
   NSURLErrorDataNotAllowed = -1020,    
   NSURLErrorRequestBodyStreamExhausted = -1021,   
   NSURLErrorFileDoesNotExist = -1100,    
   NSURLErrorFileIsDirectory = -1101,    
   NSURLErrorNoPermissionsToReadFile = -1102,    
   NSURLErrorSecureConnectionFailed = -1200,   
   NSURLErrorServerCertificateHasBadDate = -1201,   
   NSURLErrorServerCertificateUntrusted = -1202,   
   NSURLErrorServerCertificateHasUnknownRoot = -1203,   
   NSURLErrorServerCertificateNotYetValid = -1204,  
   NSURLErrorClientCertificateRejected = -1205,   
   NSURLErrorClientCertificateRequired = -1206,   
   NSURLErrorCannotLoadFromNetwork = -2000,    
   NSURLErrorCannotCreateFile= -3000,   
   NSURLErrorCannotOpenFile = -3001,   
   NSURLErrorCannotCloseFile = -3002,    
   NSURLErrorCannotWriteToFile = -3003,    
   NSURLErrorCannotRemoveFile = -3004,    
   NSURLErrorCannotMoveFile = -3005,   
   NSURLErrorDownloadDecodingFailedMidStream = -3006,   
   NSURLErrorDownloadDecodingFailedToComplete = -3007 
   }

问题 1:为什么 Apple 使用负值作为错误代码？有什么具体原因吗？

问题 2:Apple 是否遵循任何模式来随机化错误代码？

Answer 1

1. 因为基于返回码，0 通常是可以的。剩下正整数和负整数。对成功代码(带有附加信息)使用正整数，对错误代码使用负值是 C 语言的普遍偏好。
2. 如您所见，错误代码已分组。未知和取消是特殊的，1000 是 HTTP 错误，1100 是访问错误，1200 是连接和证书错误，2000 是网络，3000 是文件和流问题。

根据问题区域对错误进行分组，并使用负数作为返回代码(因为返回负数通常会被解释为错误)。