-[__NSArrayM objectAtIndex:] Issue - ios

Question

I have a little bit problem with -[__NSArrayM objectAtIndex:]: index 6 beyond bounds [0 .. 4]' How can I show (null) If I don't have data.
Here's code
-(UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath{
if ([[bookList objectAtIndex:indexPath.item]quiz_url]==[[bookList objectAtIndex:6]quiz_url]) {// This one is problem, I have `objectAtIndex:` only 0 - 5 .
// quiz_all = [[bookList objectAtIndex:indexPath.item]quiz_url];
_getQuiz6 = [[bookList objectAtIndex:6]quiz_url];
NSLog(#" test quiz6 = %#",_getQuiz6); //It's possible? Can I print `(null)` if no data.
}
...
and
-(NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section{
return [bookList count];
}
I don't have data [[bookList objectAtIndex:6]quiz_url] on webservice.

Answer 1

There's plenty of ways you could go around this. One way to deal with it, is using "placeholder" objects to pad the content, for example, NSNull. Or you could modify your Book object and add a property like isLoaded.
Whatever method you choose, then (sticking with the NSNull);
- (UICollectionViewCell*)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath
{
// Whatever code you have
Book *book = [bookList objectAtIndex:indexPath.item];
// NSNull is a singleton, you can safely do pointer comparison
if (book == [NSNull null])
{
// Show loading or something in the cell
cell.loadingOrSomething = YES;
// Return the cell here
return cell;
}
// book wasn't NSNull, then proceed with the rest of stuff
NSURL *url = [book quiz_url];
cell.loadingOrSomething = NO;
return cell;
}

Answer 2

You can use a category if you want. Somewhere in a header include this:
#interface NSArray (custom)
-(id)quizURLAtIndex:(int)index;
#end
and in a .m file you add this:
#implementation NSArray (custom)
-(id)quizURLAtIndex:(int)index{
if(index >= self.count) return nil;
else return [[self objectAtIndex:index] quiz_url];
}
#end
And from now on, whenever you want, you can call [bookList quizURLAtIndex:indexPath.item] instead of [[bookList objectAtIndex:indexPath.row] quiz_url]