IOS:如何检查json对象不为空

Question

当某些 json 为 null 时，即使我尝试先检查它，我也会收到以下代码的错误:

编辑:前面的代码:

NSData* data = [NSData dataWithContentsOfURL: kItemsURL];
            //previous line grabed data from api.
            if (data) {
                [self performSelectorOnMainThread:@selector(fetchData:) withObject:data waitUntilDone:YES];
}
- (void)fetchData:(NSData *)jsonFeed {
     NSError* error;
        NSDictionary* json = [NSJSONSerialization JSONObjectWithData:jsonFeed                                                           options:kNilOptions                                                             error:&error];

//Original code provided
    if (![[json objectForKey:@"items"] isKindOfClass:[NSNull class]]) {
            NSLog(@"got here");
            NSLog(@"json%@",json);
            latestItems = [[json objectForKey:@"items"]mutableCopy];
    }

有没有更好的方法来检查Json不为空？

这是错误输出:

2016-05-03 13:05:43.820 testApp[407:60b] got here
2016-05-03 13:05:43.821 testApp[407:60b] json{
    items = "<null>";
}
NSNull mutableCopyWithZone:]: unrecognized selector sent to instance 0x3ac26a70
2016-05-03 13:05:43.825 ChallengeU[407:60b] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[NSNull mutableCopyWithZone:]: unrecognized selector sent to instance 0x3ac26a70'  

Answer 1

if (![json[@"items"] isEqual:[NSNull null]]) {
//do your stuff in here

}