UIHostingConfiguration+CellSelected.swift

import UIKit
import SwiftUI

final class TraitSelectionState: UITraitDefinition, UITraitBridgedEnvironmentKey {
    static func read(from traitCollection: UITraitCollection) -> Bool {
        traitCollection[TraitSelectionState.self]
    }
    
    static func write(to mutableTraits: inout any UIMutableTraits, value: Bool) {
        fatalError("Forbidden")
    }
    
    static let defaultValue = false
    static let identifier = "TraitSelectionState"
    static let name = "TraitSelectionState"
}

final class CollectionViewCell: UICollectionViewCell {
    override var traitCollection: UITraitCollection {
        super.traitCollection.replacing(TraitSelectionState.self, value: isSelected)
    }
    
    override var configurationState: UICellConfigurationState {
        var state = super.configurationState
        state.traitCollection = state.traitCollection.replacing(TraitSelectionState.self, value: isSelected)
        
        return state
    }
    
    override func updateConfiguration(using state: UICellConfigurationState) {
        var state = state
        state.traitCollection = state.traitCollection.replacing(TraitSelectionState.self, value: isSelected)
        
        super.updateConfiguration(using: state)
    }
}

extension EnvironmentValues {
    var isSelected: Bool {
        get {
            self[TraitSelectionState.self]
        }
    }
}

struct ContentView: View {
    @Environment(\.isSelected) private var isSelected
    
    var body: some View {
        Group {
            if isSelected {
                Color.blue
            } else {
                Color.red
            }
        }
            .frame(height: 44.0)
            .onChange(of: isSelected, initial: false) { oldValue, newValue in
                print(newValue)
            }
    }
}

final class CollectionViewController: UICollectionViewController {
    private let cellRegistration: UICollectionView.CellRegistration<CollectionViewCell, Void> = .init { cell, indexPath, itemIdentifier in
        cell.contentConfiguration = UIHostingConfiguration {
            ContentView()
        }
    }
    
    override func numberOfSections(in collectionView: UICollectionView) -> Int {
        1
    }
    
    override func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        100
    }
    
    override func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        collectionView.dequeueConfiguredReusableCell(using: cellRegistration, for: indexPath, item: ())
    }
}