自定义NSError

domain：错误域 
code：错误编码
userInfo：错误原因

NSString *domain = @"xxxxxx";
NSString *desc = NSLocalizedString(@"xxx", @"xxx");//NSLocalizedString国际化
NSDictionary *userInfo = @{NSLocalizedDescriptionKey : desc };

NSError *error = [NSError errorWithDomain:domain code:-101 userInfo:userInfo];