所有错误代码都在文档（link）的“CFNetwork Errors Codes References”中
CFURL和CFURLConnection错误的小提取：

kCFURLErrorUnknown   = -998,
  kCFURLErrorCancelled = -999,
  kCFURLErrorBadURL    = -1000,
  kCFURLErrorTimedOut  = -1001,
  kCFURLErrorUnsupportedURL = -1002,
  kCFURLErrorCannotFindHost = -1003,
  kCFURLErrorCannotConnectToHost    = -1004,
  kCFURLErrorNetworkConnectionLost  = -1005,
  kCFURLErrorDNSLookupFailed        = -1006,
  kCFURLErrorHTTPTooManyRedirects   = -1007,
  kCFURLErrorResourceUnavailable    = -1008,
  kCFURLErrorNotConnectedToInternet = -1009,
  kCFURLErrorRedirectToNonExistentLocation = -1010,
  kCFURLErrorBadServerResponse             = -1011,
  kCFURLErrorUserCancelledAuthentication   = -1012,
  kCFURLErrorUserAuthenticationRequired    = -1013,
  kCFURLErrorZeroByteResource        = -1014,
  kCFURLErrorCannotDecodeRawData     = -1015,
  kCFURLErrorCannotDecodeContentData = -1016,
  kCFURLErrorCannotParseResponse     = -1017,
  kCFURLErrorInternationalRoamingOff = -1018,
  kCFURLErrorCallIsActive               = -1019,
  kCFURLErrorDataNotAllowed             = -1020,
  kCFURLErrorRequestBodyStreamExhausted = -1021,
  kCFURLErrorFileDoesNotExist           = -1100,
  kCFURLErrorFileIsDirectory            = -1101,
  kCFURLErrorNoPermissionsToReadFile    = -1102,
  kCFURLErrorDataLengthExceedsMaximum   = -1103,

我有类似的问题，在我的情况下似乎与网络连接：
错误域=NSURLErrorDomain Code=-1001“请求超时。”
检查事项：

• 您的服务器是否有可能在某个时间限制内无法响应？60秒还是4分钟
• 您的设备是否有可能正在切换网络（WiFi、3G、VPN）？
• 客户（Client）服务器）是否正在等待验证？

对不起，不知道如何修复。只是调试这个，试图找出问题所在（-1021，-1001，-1009）

**更新：**Google搜索很好地找到了这个：

• -1001 TimedOut -花费的时间比分配的超时时间长。
• -1003 CannotFindHost -找不到主机。
• -1004 CannotConnectToHost -主机不允许我们建立连接。

参见NSURLError.h定义

NSURLErrorUnknown =             -1,
NSURLErrorCancelled =           -999,
NSURLErrorBadURL =              -1000,
NSURLErrorTimedOut =            -1001,
NSURLErrorUnsupportedURL =          -1002,
NSURLErrorCannotFindHost =          -1003,
NSURLErrorCannotConnectToHost =         -1004,
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,
NSURLErrorAppTransportSecurityRequiresSecureConnection NS_ENUM_AVAILABLE(10_11, 9_0) = -1022,
NSURLErrorFileDoesNotExist =        -1100,
NSURLErrorFileIsDirectory =         -1101,
NSURLErrorNoPermissionsToReadFile =     -1102,
NSURLErrorDataLengthExceedsMaximum NS_ENUM_AVAILABLE(10_5, 2_0) =   -1103,

// SSL errors
NSURLErrorSecureConnectionFailed =      -1200,
NSURLErrorServerCertificateHasBadDate =     -1201,
NSURLErrorServerCertificateUntrusted =  -1202,
NSURLErrorServerCertificateHasUnknownRoot = -1203,
NSURLErrorServerCertificateNotYetValid =    -1204,
NSURLErrorClientCertificateRejected =   -1205,
NSURLErrorClientCertificateRequired =   -1206,
NSURLErrorCannotLoadFromNetwork =       -2000,

// Download and file I/O errors
NSURLErrorCannotCreateFile =        -3000,
NSURLErrorCannotOpenFile =          -3001,
NSURLErrorCannotCloseFile =         -3002,
NSURLErrorCannotWriteToFile =       -3003,
NSURLErrorCannotRemoveFile =        -3004,
NSURLErrorCannotMoveFile =          -3005,
NSURLErrorDownloadDecodingFailedMidStream = -3006,
NSURLErrorDownloadDecodingFailedToComplete =-3007,

NSURLErrorInternationalRoamingOff NS_ENUM_AVAILABLE(10_7, 3_0) =         -1018,
NSURLErrorCallIsActive NS_ENUM_AVAILABLE(10_7, 3_0) =                    -1019,
NSURLErrorDataNotAllowed NS_ENUM_AVAILABLE(10_7, 3_0) =                  -1020,
NSURLErrorRequestBodyStreamExhausted NS_ENUM_AVAILABLE(10_7, 3_0) =      -1021,

NSURLErrorBackgroundSessionRequiresSharedContainer NS_ENUM_AVAILABLE(10_10, 8_0) = -995,
NSURLErrorBackgroundSessionInUseByAnotherProcess NS_ENUM_AVAILABLE(10_10, 8_0) = -996,
NSURLErrorBackgroundSessionWasDisconnected NS_ENUM_AVAILABLE(10_10, 8_0)= -997,

我在我的项目中使用以下方法

-(NSArray*)networkErrorCodes
{
    static NSArray *codesArray;
    if (![codesArray count]){
        @synchronized(self){
            const int codes[] = {
                //kCFURLErrorUnknown,     //-998
                //kCFURLErrorCancelled,   //-999
                //kCFURLErrorBadURL,      //-1000
                //kCFURLErrorTimedOut,    //-1001
                //kCFURLErrorUnsupportedURL, //-1002
                //kCFURLErrorCannotFindHost, //-1003
                kCFURLErrorCannotConnectToHost,     //-1004
                kCFURLErrorNetworkConnectionLost,   //-1005
                kCFURLErrorDNSLookupFailed,         //-1006
                //kCFURLErrorHTTPTooManyRedirects,    //-1007
                kCFURLErrorResourceUnavailable,     //-1008
                kCFURLErrorNotConnectedToInternet,  //-1009
                //kCFURLErrorRedirectToNonExistentLocation,   //-1010
                kCFURLErrorBadServerResponse,               //-1011
                //kCFURLErrorUserCancelledAuthentication,     //-1012
                //kCFURLErrorUserAuthenticationRequired,      //-1013
                //kCFURLErrorZeroByteResource,        //-1014
                //kCFURLErrorCannotDecodeRawData,     //-1015
                //kCFURLErrorCannotDecodeContentData, //-1016
                //kCFURLErrorCannotParseResponse,     //-1017
                kCFURLErrorInternationalRoamingOff, //-1018
                kCFURLErrorCallIsActive,                //-1019
                //kCFURLErrorDataNotAllowed,              //-1020
                //kCFURLErrorRequestBodyStreamExhausted,  //-1021
                kCFURLErrorFileDoesNotExist,            //-1100
                //kCFURLErrorFileIsDirectory,             //-1101
                kCFURLErrorNoPermissionsToReadFile,     //-1102
                //kCFURLErrorDataLengthExceedsMaximum,     //-1103
            };
            int size = sizeof(codes)/sizeof(int);
            NSMutableArray *array = [[NSMutableArray alloc] init];
            for (int i=0;i<size;++i){
                [array addObject:[NSNumber numberWithInt:codes[i]]];
            }
            codesArray = [array copy];
        }
    }
    return codesArray;
}

然后，我只是检查错误代码，并显示警报，如果它是在列表中

if ([[self networkErrorCodes] containsObject:[NSNumber
numberWithInt:[error code]]]){ 
// Fire Alert View Here
}

但是正如你所看到的，我注解掉了我认为不符合我对“没有互联网”的定义的代码。例如代码-1012（验证失败）。您可以根据需要编辑列表。
在我的项目中，我使用它在用户名/密码输入从用户。在我看来（物理）网络连接错误可能是在基于网络的应用程序中显示警报视图的唯一原因。在任何其他情况下（例如：不正确的用户名/密码对）我更喜欢做一些自定义的用户友好的动画，或者只是重复失败的尝试再次没有任何注意的用户。特别是如果用户没有明确地发起网络呼叫。
请参考martinezdelariva提供的文档链接。

我发现了一个新的错误代码，上面没有记录：CFNetworkErrorCode-1022

Error Domain=NSURLErrorDomain Code=-1022 "The resource could not be loaded because the App Transport Security policy requires the use of a secure connection."

我在文档中发现了这个页面，其中有一个针对NSURLErrorDomain下所有错误代码的objective-c枚举。
https://developer.apple.com/library/ios/documentation/Cocoa/Reference/Foundation/Miscellaneous/Foundation_Constants/index.html#//apple_ref/doc/constant_group/URL_Loading_System_Error_Codes

以下网站对于查找未记录或难以找到的Apple API错误代码也非常有用：
https://www.osstatus.com/
您可以只提供错误代码（如-1001或kCFURLErrorTimedOut），甚至是您正在使用的Framework或API（如CFNetwork，NSURL或AVAudioSession），该网站将列出所有与您的搜索匹配的潜在错误，显示错误名称，相关的Framework和定义错误的头文件。