如何在Objective-C中比较字符串？

Question

I am having problems in comparing two string objects in objective-c. Here is my situation:

I have two NSString objects in my view controller as follow shown in my code below, in my .h file:

@property(nonatomic,retain) NSString *detailFacility;

in my .m file in viewDidLoad function:

- (void)viewDidLoad
{

NSData *facilityZoneURL = [NSData dataWithContentsOfURL:[NSURL URLWithString:[NSString stringWithFormat:@"some URL..."]]];  
NSError *error;
NSDictionary *facilityZoneDict = [NSJSONSerialization JSONObjectWithData:facilityZoneURL options:kNilOptions error:&error];

NSArray *facilityZoneData = [facilityZoneDict objectForKey:@"Data"];

if (![facilityZoneData isKindOfClass:[NSArray class]]) {
    //JSON does not returned the Dictionary;
}

facilityZoneArray = [[NSMutableArray alloc] init];
NSLog(@"%@",detailFacility);
for (NSDictionary *item in facilityZoneData) {
    NSString *zoneFacilityID = [NSString stringWithFormat:@"%@",[item objectForKey:@"FacilityId"]]; 

    NSLog(@"Facility ID: %@ --- Zone ID: %@",detailFacility,zoneFacilityID);

    NSLog(@"%@",[zoneFacilityID isEqualToString:detailFacility]? @"YES" : @"NO");
    if ([zoneFacilityID isEqualToString:detailFacility]) {
        NSLog(@"object added");
    }
}

But the problem is it is not comparing the strings as it is surely matches as some position.

here is my NSLOG situation:

2012-04-02 12:12:42.998 CarbonIndex[11078:207] Facility ID: 1056 --- Zone ID: 1056
2012-04-02 12:12:42.999 CarbonIndex[11078:207] NO

As you can see that both the string are accurately matched, but the if-condition does not execute, Tell me what I am missing in it.

Answer 1

It's likely an encoding issue. Try using something like this and see if it helps:

NSLog(@"%@",[zoneFacilityID compare:detailFacility]==NSOrderedSame? @"YES" : @"NO");

Compare works better with different encoding normalizations. See details here: http://weblog.bignerdranch.com/?p=334

Answer 2

More likely than not, one of your strings is not a string. It is an NSNumber and, thus, trying to do a string comparison is failing.

Try changing your logging to verify this:

    NSLog(@"Facility ID: %@ --- Zone ID: %@",[detailFacility class],
              [zoneFacilityID class]);

If that is the case, then you'll likely want to change whatever code that is currently expected to store an NSString to storing an NSNumber, then use isEqual: on the number instances (as that will be faster and more straightforward than number->string conversions everywhere).