SWIFTUI.swift

import Foundation
import SwiftUI

struct ContentView: View {
	@State private var model = Model()

    var body: some View {
		ZStack {
			CustomCollectionView(lastSelectedIndex: $model.index)
			IndexPreviewer(model: model)
		}
    }
}

struct IndexPreviewer: View {
	@ObservedObject var model: Model

	var body: some View {
		Text("Current Selected Index \(model.index)")
	}
}

class Model: ObservableObject {
	@Published var index = -1
}

struct CustomCollectionView: UIViewRepresentable {
    //@Binding var lastSelectedIndex : Int
    var lastSelectedIndex: Binding<Int>

    func makeUIView(context: Context) -> UICollectionView {
        let flowLayout = UICollectionViewFlowLayout()
        flowLayout.itemSize = CGSize(width: 400, height: 300)
        let collectionView = UICollectionView(frame: .zero, collectionViewLayout: flowLayout)
        collectionView.register(CustomCollectionViewCell.self, forCellWithReuseIdentifier: CustomCollectionViewCell.reuseId)
        collectionView.delegate = context.coordinator
        collectionView.dataSource = context.coordinator
        collectionView.backgroundColor = .systemBackground
        collectionView.isDirectionalLockEnabled = true
        
        collectionView.backgroundColor = UIColor.black
        collectionView.showsVerticalScrollIndicator = false
        collectionView.showsHorizontalScrollIndicator = false
        collectionView.alwaysBounceVertical = false
        return collectionView
    }

    func updateUIView(_ uiView: UICollectionView, context: Context) {
        uiView.reloadData()
    }

    func makeCoordinator() -> CustomCoordinator {
        CustomCoordinator(self)
    }
}

class CustomCoordinator: NSObject, UICollectionViewDataSource, UICollectionViewDelegate {
    var parent:CustomCollectionView
    
    init(_ parent:CustomCollectionView) {
        self.parent = parent
    }
    
    func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        100
    }

    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {

        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: CustomCollectionViewCell.reuseId, for: indexPath) as! CustomCollectionViewCell
        cell.backgroundColor = UIColor.red
        cell.label.text = "My Index is \(indexPath.row)"
        NSLog("Called for Index \(indexPath.row)")
        return cell
    }
    
    func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
        parent.lastSelectedIndex.wrappedValue = indexPath.row
    }
}

class CustomCollectionViewCell: UICollectionViewCell {
    static let reuseId = "customCell"
    let label = UILabel()

    override init(frame: CGRect) {
        super.init(frame: frame)
        label.numberOfLines = 0
        contentView.addSubview(label)
        label.translatesAutoresizingMaskIntoConstraints = false
        label.topAnchor.constraint(equalTo: contentView.topAnchor).isActive = true
        label.leadingAnchor.constraint(equalTo: contentView.leadingAnchor).isActive = true
        label.trailingAnchor.constraint(equalTo: contentView.trailingAnchor).isActive = true
        label.bottomAnchor.constraint(equalTo: contentView.bottomAnchor).isActive = true
    }

    required init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
}

struct ContentView_Previews: PreviewProvider {
    static var previews: some View {
        ContentView()
    }
}