Cells are hidden using CollectionView - ios

Question

I have a Navigation Controller pushing to a Collection View Controller. This collectionView has an NSArray of images, and I'm sure there are some elements in the collectionView using the method visibleCells.
But when I launch it there is no displaying cells.
Here is my code :
- (void)viewDidLoad
{
[super viewDidLoad];
images = [NSArray arrayWithObjects:#"angry_birds_cake.jpg", #"creme_brelee.jpg", #"egg_benedict.jpg", #"full_breakfast.jpg", #"green_tea.jpg", #"ham_and_cheese_panini.jpg", #"ham_and_egg_sandwich.jpg", #"hamburger.jpg", #"instant_noodle_with_egg.jpg", #"japanese_noodle_with_pork.jpg", #"mushroom_risotto.jpg", #"noodle_with_bbq_pork.jpg", #"starbucks_coffee.jpg", #"thai_shrimp_cake.jpg", #"vegetable_curry.jpg", #"white_chocolate_donut.jpg", nil];
}
- (NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section {
return images.count;
}
- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath{
static NSString *identifier = #"Cell";
UICollectionViewCell *cell;
[collectionView registerClass:[UICollectionViewCell class] forCellWithReuseIdentifier:#"Cell"];
cell = [collectionView dequeueReusableCellWithReuseIdentifier:identifier forIndexPath:indexPath];
NSArray *tab = [collectionView visibleCells];
for (int i = 0; i < [tab count]; ++i)
{
NSLog(#"%d", i);
}
[collectionView setBackgroundColor:[UIColor blueColor]];
UIImageView *imageView = (UIImageView *)[cell viewWithTag:100];
imageView.image = [UIImage imageNamed:[images objectAtIndex:indexPath.row]];
return cell;
}
Where am I wrong ? Thanks a lot.