一、NSError是系统错误信息类

//两种初始化方法：其中，domain 不能为空 dict可以为空

- (instancetype)initWithDomain:(NSErrorDomain)domain code:(NSInteger)code userInfo:(nullable NSDictionary *)dict;

+ (instancetype)errorWithDomain:(NSErrorDomain)domain code:(NSInteger)code userInfo:(nullable NSDictionary *)dict;

@property (readonly, copy) NSErrorDomain domain;//错误域

错误域主要有四个，对于Carbon框架的Error，归于OSStatus domain(NSOSStatusErrorDomain)，对于POSIX error，归于NSPOSIXErrorDomain，而对于我们的iOS开发，一般使用NSCocoaErrorDomain。NSError.h定义了四个domain

{

// Predefined domain for errors from most AppKit and Foundation APIs.

FOUNDATION_EXPORT NSErrorDomain const NSCocoaErrorDomain;

// Other predefined domains; value of "code" will correspond to preexisting values in these domains.

FOUNDATION_EXPORT NSErrorDomain const NSPOSIXErrorDomain;

FOUNDATION_EXPORT NSErrorDomain const NSOSStatusErrorDomain;

FOUNDATION_EXPORT NSErrorDomain const NSMachErrorDomain;

}

@property (readonly) NSInteger code;//错误代码

@property (readonly, copy) NSDictionary *userInfo;//错误信息

@property (readonly, copy) NSString *localizedDescription;//获取本地化描述

@property (nullable, readonly, copy) NSString *localizedFailureReason;//获取失败原因

@property (nullable, readonly, copy) NSString *localizedRecoverySuggestion;//获取恢复建议

@property (nullable, readonly, copy) NSArray *localizedRecoveryOptions;本地恢复建议

@property (nullable, readonly, strong) id recoveryAttempter;

@property (nullable, readonly, copy) NSString *helpAnchor;

预定义的userinfo键名

NSString *const NSUnderlyingErrorKey;//推荐的标准方式，通用键

NSString *const NSLocalizedDescriptionKey;             // 详细描述键

NSString *const NSLocalizedFailureReasonErrorKey;      // 失败原因键

NSString *const NSLocalizedRecoverySuggestionErrorKey; //恢复建议键

NSString *const NSLocalizedRecoveryOptionsErrorKey;    // 恢复选项键

//其他键

NSString *const NSRecoveryAttempterErrorKey;

NSString *const NSHelpAnchorErrorKey;

NSString *const NSStringEncodingErrorKey ;

NSString *const NSURLErrorKey;

NSString *const NSFilePathErrorKey;

用法示例：

NSDictionary *userInfo1 = [NSDictionary dictionaryWithObjectsAndKeys:@"由于文件不存在，无法打开", NSLocalizedDescriptionKey, @"失败原因：文件不存在", NSLocalizedFailureReasonErrorKey, @"恢复建议：请创建该文件",NSLocalizedRecoverySuggestionErrorKey,nil];

NSError *error = [[NSError alloc] initWithDomain:NSCocoaErrorDomain code:4 userInfo:userInfo1];//此处code是4，对照下面对照表4代表文件不存在。userinfo传userinfo1 查看自定义打印。userinfo传nil，查看本地化描述。

NSLog(@"========%@",[error localizedDescription]);

NSLog(@"========%@",[error localizedFailureReason]);

NSLog(@"========%@",[error localizedRecoverySuggestion]);

二、NSError错误code对照表

Foundation Constants Reference

NSError Codes

NSError codes in the Cocoa error domain.

enum {

NSFileNoSuchFileError = 4,

NSFileLockingError = 255,

NSFileReadUnknownError = 256,

NSFileReadNoPermissionError = 257,

NSFileReadInvalidFileNameError = 258,

NSFileReadCorruptFileError = 259,

NSFileReadNoSuchFileError = 260,

NSFileReadInapplicableStringEncodingError = 261,

NSFileReadUnsupportedSchemeError = 262,

NSFileReadTooLargeError = 263,

NSFileReadUnknownStringEncodingError = 264,

NSFileWriteUnknownError = 512,

NSFileWriteNoPermissionError = 513,

NSFileWriteInvalidFileNameError = 514,

NSFileWriteInapplicableStringEncodingError = 517,

NSFileWriteUnsupportedSchemeError = 518,

NSFileWriteOutOfSpaceError = 640,

NSFileWriteVolumeReadOnlyError = 642m

NSKeyValueValidationError = 1024,

NSFormattingError = 2048,

NSUserCancelledError = 3072,

NSFileErrorMinimum = 0,

NSFileErrorMaximum = 1023,

NSValidationErrorMinimum = 1024,

NSValidationErrorMaximum = 2047,

NSFormattingErrorMinimum = 2048,

NSFormattingErrorMaximum = 2559,

NSPropertyListReadCorruptError = 3840,

NSPropertyListReadUnknownVersionError = 3841,

NSPropertyListReadStreamError = 3842,

NSPropertyListWriteStreamError = 3851,

NSPropertyListErrorMinimum = 3840,

NSPropertyListErrorMaximum = 4095

NSExecutableErrorMinimum = 3584,

NSExecutableNotLoadableError = 3584,

NSExecutableArchitectureMismatchError = 3585,

NSExecutableRuntimeMismatchError = 3586,

NSExecutableLoadError = 3587,

NSExecutableLinkError = 3588,

NSExecutableErrorMaximum = 3839,

}

URL Loading System Error Codes

These values are returned as the error code property of an NSError object with the domain “NSURLErrorDomain”.

typedef enum

{

NSURLErrorUnknown = -1,

NSURLErrorCancelled = -999,

NSURLErrorBadURL = -1000,

NSURLErrorTimedOut = -1001,

NSURLErrorUnsupportedURL = -1002,

NSURLErrorCannotFindHost = -1003,

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,

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

}

三、自定义NSError

系统的NSError是可以自己定制的，以下提供代码来实现并表示如何使用：

YXError.h 与 YXError.m

//

//  YXError.h

//  CustomYXError

//

//  Copyright (c) 2014年 Y.X. All rights reserved.

//

#import

// 自行添加错误码

typedef enum : NSUInteger {

Crash     = -10000,

DisConnect,

Unknow,

} YXErrorCode;

@interface YXError : NSObject

+ (NSError *)errorCode:(YXErrorCode)code userInfo:(NSDictionary *)dic;

+ (NSString *)transformCodeToStringInfo:(YXErrorCode)code;

@end

//

//  YXError.m

//  CustomYXError

//

//  Copyright (c) 2014年 Y.X. All rights reserved.

//

#import "YXError.h"

static NSDictionary *errorDictionary = nil;

@implementation YXError

+ (void)initialize

{

if (self == [YXError class])

{

errorDictionary = \

@{

/* code        :        errorWithDomain */

/* ==================================== */

@(Crash)       :@"Crash",

@(DisConnect)  :@"DisConnect",

@(Unknow)      :@"Unknow",

/* ==================================== */

};

}

}

+ (NSError *)errorCode:(YXErrorCode)code userInfo:(NSDictionary *)dic

{

return [NSError errorWithDomain:errorDictionary[@(code)]

code:code

userInfo:dic];

}

+ (NSString *)transformCodeToStringInfo:(YXErrorCode)code

{

return errorDictionary[@(code)];

}

@end

以下是使用的代码：

//

//  AppDelegate.m

//  NSError

//

//  Copyright (c) 2014年 YouXianMing. All rights reserved.

//

#import "AppDelegate.h"

#import "YXError.h"

@implementation AppDelegate

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions

{

// 定制一个NSError

NSError *error = [YXError errorCode:Crash

userInfo:nil];

NSLog(@"%@", error);

// 翻译一个NSError(将code值翻译成字符串)

NSLog(@"%@", [YXError transformCodeToStringInfo:-10000]);

return YES;

}

@end