一、NSError 是系统错误信息类
1. 两种初始化方法:其中，dimain(域)不能为空，dict可以为空
//实例方法
- (instancetype)initWithDomain:(NSErrorDomain)domain code:(NSInteger)code userInfo:(nullable NSDictionary *)dict;
//类方法初始化
+ (instancetype)errorWithDomain:(NSErrorDomain)domain code:(NSInteger)code userInfo:(nullable NSDictionary *)dict;
2. 错误域(第一个参数)
//属性
@property (readonly, copy) NSErrorDomain domain;//错误域
@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;
错误域主要有四个：
- NSCocoaErrorDomain: 针对我们iOS开发(我们主要用这个)
- NSOSStatusErrorDomain：针对Carbon框架的Error
- NSPOSIXErrorDomain：针对POSIX的Error
NS_ASSUME_NONNULL_BEGIN
// 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;
4. userinfo(第三个参数)
第三个参数是一个字典，其中预定义的userinfo键名如下
//常用键
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 *userInfo = @{
NSLocalizedDescriptionKey:@"由于文件不存在，无法打开",
NSLocalizedFailureReasonErrorKey:@"失败原因：文件不存在",
NSLocalizedRecoverySuggestionErrorKey:@"恢复建议：请创建该文件"
};
//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。
NSError *error = [[NSError alloc] initWithDomain:NSCocoaErrorDomain code:4 userInfo:userInfo1];
NSLog(@"========%@",[error localizedDescription]);
NSLog(@"========%@",[error localizedFailureReason]);
NSLog(@"========%@",[error localizedRecoverySuggestion]);
打印结果：
2019-02-28 11:50:40.469721+0800 emoji maker[57155:1624717] ========由于文件不存在，无法打开
2019-02-28 11:50:40.469816+0800 emoji maker[57155:1624717] ========失败原因：文件不存在
2019-02-28 11:50:40.469881+0800 emoji maker[57155:1624717] ========恢复建议：请创建该文件
3. 错误代码(第二个参数附: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
}
参考文章：
iOS NSError详解 NSError错误code对照表 自定义、定制NSError 一看就懂