How do we know the specific item in cellForRow method when compositional layout is used

Question

I have created a collection view with compositional layout, Below is the code I have used for creating the layout.

    func getCompositionalLayout() -> UICollectionViewCompositionalLayout {
        
        let item = NSCollectionLayoutItem(layoutSize: NSCollectionLayoutSize(widthDimension: .fractionalWidth(1), heightDimension: .fractionalHeight(1/3)))
        item.contentInsets = NSDirectionalEdgeInsets(top: 1, leading: 1, bottom: 1, trailing: 1)


        //--------- Group 1 ---------//
        let group1Item1 = NSCollectionLayoutItem(layoutSize: NSCollectionLayoutSize(widthDimension: .fractionalWidth(1/2), heightDimension: .fractionalHeight(1)))
        group1Item1.contentInsets = NSDirectionalEdgeInsets(top: 1, leading: 1, bottom: 1, trailing: 1)
        


        let nestedGroup1Item1 = NSCollectionLayoutItem(layoutSize: NSCollectionLayoutSize(widthDimension: .fractionalWidth(1), heightDimension: .fractionalHeight(1/2)))
        nestedGroup1Item1.contentInsets = NSDirectionalEdgeInsets(top: 1, leading: 1, bottom: 1, trailing: 1)

         let nestedGroup2Item1 = NSCollectionLayoutItem(layoutSize: NSCollectionLayoutSize(widthDimension: .fractionalWidth(1/2), heightDimension: .fractionalHeight(1)))
        nestedGroup2Item1.contentInsets = NSDirectionalEdgeInsets(top: 1, leading: 1, bottom: 1, trailing: 1)
        
        let nestedGroup2 = NSCollectionLayoutGroup.horizontal(layoutSize: NSCollectionLayoutSize(widthDimension: .fractionalWidth(1), heightDimension: .fractionalHeight(1/2)), subitems: [nestedGroup2Item1])
        
        let nestedGroup1 = NSCollectionLayoutGroup.vertical(layoutSize: NSCollectionLayoutSize(widthDimension: .fractionalWidth(1/2), heightDimension: .fractionalHeight(1)), subitems: [nestedGroup1Item1, nestedGroup2])

        let group1 = NSCollectionLayoutGroup.horizontal(layoutSize: NSCollectionLayoutSize(widthDimension: .fractionalWidth(1), heightDimension: .fractionalHeight(1/3)), subitems: [group1Item1, nestedGroup1])


        //--------- Group 2 ---------//
        let group2Item1 = NSCollectionLayoutItem(layoutSize: NSCollectionLayoutSize(widthDimension: .fractionalWidth(1/3), heightDimension: .fractionalHeight(1)))
        group2Item1.contentInsets = NSDirectionalEdgeInsets(top: 1, leading: 1, bottom: 1, trailing: 1)

        let group2 = NSCollectionLayoutGroup.horizontal(layoutSize: NSCollectionLayoutSize(widthDimension: .fractionalWidth(1), heightDimension: .fractionalHeight(1/3)), subitems: [group2Item1])


        //--------- Container Group ---------//
        let containerGroup = NSCollectionLayoutGroup.vertical(layoutSize: NSCollectionLayoutSize(widthDimension: .fractionalWidth(1), heightDimension: .absolute(600)), subitems: [item, group1, group2])

        let section = NSCollectionLayoutSection(group: containerGroup)
        let layout = UICollectionViewCompositionalLayout(section: section)
        return layout

}

with this block of code my collection view look like this

enter image description here

Now my question is how do I know the RED CELL every time it occurs in cellForItem method so that I can show the different content in it. (same like Instagram shows the video in larger cell on their search page).

Am unable to identify the red cell (Its in Group 1 with name group1Item1)

Answer 1

Observe that your layout "repeats" every 8 cells. i.e. it has a period of 8. It's always these 8 cells repeating themselves:

We can see that the red cell you want to identify is the second one in this sequence of 8 cells. The red cell would be at index 1, 9, 17, 25 and so on. Therefore, we can simply check the remainder of dividing by 8:

if indexPath.row % 8 == 1 {
    // this is the red cell
} else {
    // something else
}