Manipulate uicollectionview inside uicollectionviewcell from uiviewcontroller

Question

I have a UIViewController containing a UICollectionView and within their UICollectionViewCell is embedded another UICollectionView structure

And visually looks like this: visually

I want to press BOTON in UIViewController and from there, change the backgroundColor of UICollectionView inside the cell of the outter UICollectionView

My UIViewController class

class ViewController: UIViewController, UICollectionViewDelegate, UICollectionViewDataSource, UICollectionViewDelegateFlowLayout {


@IBOutlet weak var scrollH: UICollectionView!

override func viewDidLoad() {
    super.viewDidLoad()
    if let flowLayout = scrollH.collectionViewLayout as? UICollectionViewFlowLayout {
        flowLayout.minimumLineSpacing = 0
    }

    setupMenuQuestion()
}

var uiview: UIView = {
    let view1 = UIView()
    view1.backgroundColor = UIColor.brown
    return view1
}()

var uibutton: UIButton = {
    let btn1 = UIButton()
    btn1.setTitle("BOTON", for: .normal)
    btn1.addTarget(self, action: #selector(presionoBoton), for: .touchUpInside)
    return btn1
}()

@objc func presionoBoton() {
    delegateExterior?.cambiarBackground()
}

var delegateExterior: ExteriorCollectionViewCellDelegate?

private func setupMenuQuestion() {
    view.addSubview(uiview)

    uiview.translatesAutoresizingMaskIntoConstraints = false
    uiview.leftAnchor.constraint(equalTo: view.leftAnchor, constant: 0).isActive = true
    uiview.rightAnchor.constraint(equalTo: view.rightAnchor, constant: 0).isActive = true
    uiview.bottomAnchor.constraint(equalTo: view.bottomAnchor, constant: 0).isActive = true
    uiview.heightAnchor.constraint(equalToConstant: 30).isActive = true

    uibutton.translatesAutoresizingMaskIntoConstraints = false
    uiview.addSubview(uibutton)
    uibutton.centerYAnchor.constraint(equalTo: uiview.centerYAnchor).isActive = true
    uibutton.centerXAnchor.constraint(equalTo: uiview.centerXAnchor).isActive = true
    uibutton.leftAnchor.constraint(equalTo: uiview.leftAnchor, constant: 7).isActive = true
    uibutton.rightAnchor.constraint(equalTo: uiview.rightAnchor, constant: -7).isActive = true
    uibutton.heightAnchor.constraint(equalTo: uiview.heightAnchor, multiplier: 0.8).isActive = true

}

func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
    return 3
}

func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
    let cellNumQuestion = collectionView.dequeueReusableCell(withReuseIdentifier: "celdaExterior", for: indexPath) as! ExteriorCollectionViewCell
    return cellNumQuestion
}

func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {
    return CGSize(width: view.frame.width, height: view.frame.height - 100)
}

}

My UICollectionViewCell Class

protocol ExteriorCollectionViewCellDelegate {
func cambiarBackground()
}

class ExteriorCollectionViewCell: UICollectionViewCell, 
UICollectionViewDataSource, UICollectionViewDelegate, 
UICollectionViewDelegateFlowLayout, ExteriorCollectionViewCellDelegate{

func cambiarBackground() {
    collectionCelda.backgroundColor = UIColor.black
}

@IBOutlet weak var collectionCelda: UICollectionView!


override init(frame: CGRect) {
    super.init(frame: frame)
    let layout: UICollectionViewFlowLayout = UICollectionViewFlowLayout()
    layout.minimumInteritemSpacing = 40
    layout.minimumLineSpacing = 40
    collectionCelda!.collectionViewLayout = layout

}

required init?(coder aDecoder: NSCoder) {
    super.init(coder: aDecoder)
}

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

func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
    var cell = UICollectionViewCell()
    cell = collectionView.dequeueReusableCell(withReuseIdentifier: "celdaInterior", for: indexPath)

    return cell
}

func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {
    return CGSize(width: frame.width - 20, height: 400)
}

func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, insetForSectionAt section: Int) -> UIEdgeInsets {

    return UIEdgeInsets(top: 30.0, left: 0.0, bottom: 30.0, right: 0.0)
}

func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, minimumLineSpacingForSectionAt section: Int) -> CGFloat {
    return 40
}

}

I have seen another post similar to my problem but I do not know how to proceed
How to access a collectionView that is embedded in a parent collectionViewCell in the main UIViewController?

Answer 1

In your case, you didn't set the delegate you've created, you should set it inside:

func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
    let cellNumQuestion = collectionView.dequeueReusableCell(withReuseIdentifier: "celdaExterior", for: indexPath) as! ExteriorCollectionViewCell
    // Setting the delegate
    delegateExterior = cellNumQuestion
    return cellNumQuestion
}

Also, in order to avoid reference-cycle set your delegateExterior pointer to be weak:

weak var delegateExterior: ExteriorCollectionViewCellDelegate?

Another solution will be to add an observer inside ExteriorCollectionViewCell and when the button is tapped and the IBAction method gets called inside your UIViewController , use post notification to pass that event into your observer.

ie:

Add the observer that will listen to your events inside your ExteriorCollectionViewCell :

 NotificationCenter.default.addObserver(forName: NSNotification.Name(rawValue: "EventForCollectionView"),
                                                               object: nil,
                                                               queue: nil) { [weak self] (_) in
// This method will be invoked when you post notification from your IBAction method inside your UIVC                                                                
self?.YourCustomMethod()
}

Send your notification event from your IBAction inside the IBAction method:

NotificationCenter.default.post(name: NSNotification.Name(rawValue: "EventForCollectionView"), object: nil)

But if the button is inside your UICollectionViewCell you can just use IBAction method inside your UICollectionViewCell and do your logic there.