How to access a collectionView that is embedded in

How to access a collectionView that is embedded in a parent collectionViewCell in the main UIViewController?

My main ViewController is a UICollectionView which houses a UICollectionViewCell called BannerCell. BannerCell has a collectionView which contains 3 cells:

Headlines cell
Image cell
Posts Cell

Within PostsCell, there is a collectionView of cells which contains posts.

I want to access the collection view within the postCell, but I can't seem to get the reference of this collectionView through a delegate.

import UIKit

protocol HomeBannerPostsCellDelegate: class {
  func homeBannerPostsCellDelegateMethod1(enabled: Bool)
}

class HomeBannerHeaderPostsCollectionCell: UICollectionViewCell {
   @IBOutlet weak var bannerPostsCollectionView: UICollectionView!
   var delegate: HomeBannerPostsCellDelegate?
}

extension HomeBannerHeaderPostsCollectionCell : UICollectionViewDataSource, UICollectionViewDelegateFlowLayout {
  func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
      let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "HomeBannerHeaderPostCollectionCell", for: indexPath) as! HomeBannerHeaderPostCollectionCell
      cell.backgroundColor = UIColor.red

      if(indexPath.item==1 || indexPath.item==3 ){
          cell.backgroundColor = UIColor.blue
          return cell
      }
      return cell
  }

  func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
    return 4
  }

  func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {
    let screenWidth = UIScreen.main.bounds.width
    let frameHeight = screenWidth*0.10
    return CGSize(width: screenWidth*0.75, height: frameHeight)
  }
}

I can already get the HomeBannerPostsCellDelegate to run the method that prints out a line in the main controller.

   if(bannerCellReuseIdentifier == widgets[indexPath.item]){
        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: bannerCellReuseIdentifier, for: indexPath) as! HomeBannerCollectionCell
        cell.backgroundColor = UIColor.lightGray
        cell.delegate=self
        cell.bannerPostsDelegate=self
        self.bannerPostsCollectionView=cell.bannerPostsCollectionView
        return cell
    }

In ViewDidLoad() method

override func viewDidLoad() {
    super.viewDidLoad()
    // Do any additional setup after loading the view, typically from a nib.

        // This view controller itself will provide the delegate methods and row data for the table view.
    collectionView.delegate = self
    collectionView.dataSource = self

    // Register XIB for Supplementary View Reuse
    let XIB = UINib.init(nibName: "SectionHeader", bundle: Bundle.main)
    collectionView.register(XIB, forSupplementaryViewOfKind: UICollectionElementKindSectionHeader, withReuseIdentifier: HeaderIdentifier)

    let layout = StickyHeadersCollectionViewFlowLayout()
    collectionView.setCollectionViewLayout(layout, animated: true)
    collectionView.backgroundColor = UIColor.white

    collectionView.contentInset = UIEdgeInsets(top: -collectionView.bounds.width * 0.20 * 2, left: 0, bottom: 0, right: 0)

    self.homeBannerPostsCellDelegateMethod1(enabled: true)

    setTimer()

}

I'm trying to get the PostsCollectionView to rotate using the setTimerMethod

 func setTimer() {
    let _ = Timer.scheduledTimer(timeInterval: 3.0, target: self, selector: #selector(autoChangeBanner), userInfo: nil, repeats: true)
}

var bannerPostIndex = 0
@objc func autoChangeBanner() {
    NSLog("autoChangeBanner")
    let indexPath = IndexPath(item: bannerPostIndex, section: 0)
    self.bannerPostsCollectionView?.scrollToItem(at: indexPath, at: .centeredVertically, animated: true)
    bannerPostIndex=bannerPostIndex+1
    if(bannerPostIndex>3){
        bannerPostIndex=0
    }
}

But bannerPostsCollectionView is nil.

Is there any way I can send the reference of bannerPostsCollectionView back to the MainController?

Thanks in advance.

In the main Controller on cell did select deligate method you will check if the tapped cell is the cell with the banner.

func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
        let cell = collectionView.dequeueReusableCellWithReuseIdentifier(reuseIdentifier, forIndexPath: indexPath)

        if let bannerCell = cell as? HomeBannerHeaderPostsCollectionCell {
              bannerCell.bannerPostsCollectionView ....
              return
          }

        //And here you do whatever you want for the other cells
    }

If so you will cast the cell as a HomeBannerHeaderPostsCollectionCell and from that you will access it's variable cell.bannerPostsCollectionView and you can do what you want