objective-c Embedded UICollectionViewController shows 0 items - ios

Question

I'm trying to have a UICollectionViewController inside my UIViewController.
Here's how I set it up
TagsCollectionViewController* tagsCollectionViewController = [[TagsCollectionViewController alloc] initWithCollectionViewLayout:[UICollectionViewLayout new]];
UIView *tagsView = tagsCollectionViewController.view;
[self.view addSubview:tagsView]; // setting up constraings too
And this is my TagsCollectionViewController
#interface TagsCollectionViewController () <UICollectionViewDelegateFlowLayout>
#end
#implementation TagsCollectionViewController
static NSString * const reuseIdentifier = #"Cell";
- (void)viewDidLoad {
[super viewDidLoad];
self.collectionView.backgroundColor = [UIColor yellowColor];
[self.collectionView registerClass:[UICollectionViewCell class] forCellWithReuseIdentifier:reuseIdentifier];
}
#pragma mark <UICollectionViewDataSource>
- (NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section {
return 20;
}
- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath {
UICollectionViewCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:reuseIdentifier forIndexPath:indexPath];
cell.backgroundColor = [UIColor redColor];
return cell;
}
#pragma mark <UICollectionViewDelegateFlowLayout>
- (CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout *)collectionViewLayout sizeForItemAtIndexPath:(NSIndexPath *)indexPath {
return CGSizeMake(50, 50);
}
#end
What's strange is that I get yellow view so my collection seems to be working, however I don't get to see any items. But when I present whole controller everything works fine. So the problem occurs only when I'm trying to embed it. What can be the issue?
EDIT: Related: Adding UICollectionViewController to UIViewController Not Working

Answer 1

It looks as if it's a problem with estimating the size of items in the collection. I was able to get results by using the following code after creating a similar example and noticing that cells weren't being requested.
#interface ViewController ()
#property (nonatomic, strong) TagsCollectionViewController *tags;
#end
#implementation ViewController
- (void)viewDidLoad {
[super viewDidLoad];
UICollectionViewFlowLayout *layout = [UICollectionViewFlowLayout new];
layout.itemSize = CGSizeMake(50.0, 50.0);
self.tags = [[TagsCollectionViewController alloc] initWithCollectionViewLayout:layout];
UIView *tagsView = self.tags.view;
[self.view addSubview:tagsView];
}