MultiCollectionViewConcept.swift

func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        
      if collectionView === self.topCollectionView{
        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "topCollectionViewCell", for: indexPath) as! TopCollectionViewCell
        return cell
      }else{
        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "bottomCollectionViewCell", for: indexPath) as! BottomCollectionViewCell
        return cell
      }
      
}