Collectionview not showing

Question

I am trying to achieve a feature that whenever I tap a button from the collectionview at the bottom, the specific value that was tapped will reflect on the collectionview in the middle. So far, I have achieved the bottom collectionview, but I am not sure what is wrong with my code that my new collectionview isn't showing.

import UIKit
class MyButtonCell: UICollectionViewCell{
    @IBOutlet weak var buttonOne: UIButton!
    @IBOutlet weak var targetButton: UIButton!
    
    
    var callback: (() -> ())?
    
    override init(frame: CGRect) {
        super.init(frame: frame)
        commonInit()
        
    }
    required init?(coder: NSCoder) {
        super.init(coder: coder)
        commonInit()
    }
    func commonInit() -> Void {
        contentView.layer.borderWidth = 1
        contentView.layer.borderColor = UIColor.black.cgColor
        
        
        
        
        
    }
    
    @IBAction func buttonTapped(_ sender: UIButton) {
        callback?()
    }
}

class StevenViewController: UIViewController, UICollectionViewDelegate, UICollectionViewDataSource,UICollectionViewDelegateFlowLayout {

    let buttonTitles: [String] = [
        "4", "6", "7", "8"
    ]
    
    var targetButtonTitles: [String] = []
    //number array
    
    @IBOutlet var collectionView: UICollectionView!
    
    @IBOutlet weak var targetCollection: UICollectionView!
    
    override func viewDidLoad() {
        super.viewDidLoad()
        collectionView.delegate = self
        collectionView.dataSource = self
        
        targetCollection.delegate = self
        targetCollection.dataSource = self
        
    }
    func numberOfSections(in collectionView: UICollectionView) -> Int {
        return 1
    }
    func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        return buttonTitles.count
        
    }
    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "myCellID", for: indexPath) as! MyButtonCell
        
        let targetCell = targetCollection.dequeueReusableCell(withReuseIdentifier: "target", for: indexPath) as! MyButtonCell

        // set the button title (and any other properties)
     
        cell.buttonOne.setTitle(buttonTitles[indexPath.item], for: [])
     

        
        // set the cell's callback closure
        cell.callback = {
            print("Button was tapped at \(indexPath)")
            self.targetButtonTitles.append(self.buttonTitles[indexPath.item])
            print(self.targetButtonTitles)
        
            targetCell.targetButton.setTitle(self.targetButtonTitles[indexPath.item], for: [])
            // do what you want when the button is tapped
        }
        

        
        return cell
    }
}

My storyboard:

What's showing in the simulator:

Answer 1

Try this out.

In your cellForItemAtIndexPath you must return both cells in order to show them both.

func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
    let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "myCellID", for: indexPath) as! MyButtonCell

    let targetCell = targetCollection.dequeueReusableCell(withReuseIdentifier: "target", for: indexPath) as! MyButtonCell

    if collectionView == self.collectionView {
       
        // Setup here your cell

        cell.callback = {
            print("Button was tapped at \(indexPath)")
            self.targetButtonTitles.append(self.buttonTitles[indexPath.item])
            print(self.targetButtonTitles)
        
            targetCell.targetButton.setTitle(self.targetButtonTitles[indexPath.item], for: [])
            // do what you want when the button is tapped
        }

        cell.buttonOne.setTitle(buttonTitles[indexPath.item], for: [])

        return cell
    } else {

        // Setup here your targetCell

        return targetCell
    }

Note that also if you have a different number of sections for each collectionView, you must return them independently.

func collectionView(collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
    if collectionView == self.collectionView {
        return 1 // Number of sections of your collectionView
    }

    return 1 // Number of sections of your targetCollection
}