I read a string from a JSON result as follows:
NSString *strResult = [[NSString alloc] initWithBytes:[data bytes] 
                                               length:[data length] 
                                             encoding:NSUTF8StringEncoding]; 
I then try to determine if the string is equal to the value "N"
if ([strResult isEqualToString:@"N"])
{ 
  [lblImageOK setHidden:YES]; 
} 
else 
{ 
  [lblImageOk setHidden:NO]; 
}
The if statement allways returns the else part, even though the result is "N". They both have the same value but the statement returns false always.
I found a way to clean the string and then check if they are equal.
NSString *strResult = [[NSString alloc] initWithBytes:[data bytes] 
                                           length:[data length] 
                                         encoding:NSUTF8StringEncoding]; 
strResult = [strResult stringByReplacingOccurrencesOfString:@"\"" withString:@""];
strResult = [strResult stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceCharacterSet]];
if ([strResult isEqualToString:@"N"])
{ 
  [lblImageOK setHidden:YES]; 
} 
else 
{ 
  [lblImageOk setHidden:NO]; 
}
来源:https://stackoverflow.com/questions/9898655/how-to-determine-if-strings-are-equal-in-objective-c