iOS - Why does this NSString comparison blow-up?

Question

I have looked at SO for similar questions, but am open to being pointed to a duplicate.

I am receiving some JSON from a site, and I want to test for a 404 response.

I have this expression:

    NSString *responseString = [json objectForKey:@"statusCode"];
NSLog(@"responseString: %@", responseString);

        NSString *myString1 = @"404";

        NSLog(@"%d", (responseString == myString1)); //0
        NSLog(@"%d", [responseString isEqual:myString1]); //0
        NSLog(@"%d", [responseString isEqualToString:myString1]); //Crash

The response string returns 404. The first and second logs result in 0, and the 3rd crashes with this log:

[__NSCFNumber isEqualToString:]: unrecognized selector sent to instance 0xb000000000001943
2015-01-29 16:23:33.302 Metro[19057:5064427] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[__NSCFNumber isEqualToString:]: unrecognized selector sent to instance 0xb000000000001943'

Answer 1

statusCode is a number, not a string. The error makes this clear by telling you that you are trying to call isEqualToString on an NSNumber.

Try this:

NSInteger responseCode = [json[@"statusCode"] integerValue];
NSInteger notFoundCode = 404;
if (responseCode == notFoundCode) {
    // process 404 error
}