supplementary_provider.swift

extension CollectionViewController {
private func supplementaryViewProvider(collectionView: UICollectionView, kind: String, indexPath: IndexPath) -> UICollectionReusableView? {
    
        if kind == "badge" {
            return badgeViewProvider(collectionView, kind, indexPath)
        } else {
            return contentSupplementaryProvider(collectionView, kind, indexPath)
        }
    }
    
    private func contentSupplementaryProvider(_ collectionView: UICollectionView, _ kind: String, _ indexPath: IndexPath) -> UICollectionReusableView? {
        
        guard let view = collectionView.dequeueReusableSupplementaryView(ofKind: kind, withReuseIdentifier: HostingControllerCollectionReusableView<AnyView>.reuseIdentifier, for: indexPath) as? HostingControllerCollectionReusableView<AnyView> else {
            fatalError("Could not load supplementary view")
        }
        
        let item = self.dataSource.itemIdentifier(for: indexPath)
        
        guard let content = self.supplementaryContent?(kind, indexPath, item) else {
            fatalError("Supplementary view content not provided for kind: \(kind), indexPath: \(indexPath). Please provide supplementaryContent closure parameter to CollectionView returning some View and provide kind in supplementaryKinds array parameter. Or remove this kind: \(kind) from layout definition.")
        }
        
        view.host(content)
        
        return view
    }
    
    private func badgeViewProvider(_ collectionView: UICollectionView, _ kind: String, _ indexPath: IndexPath) -> UICollectionReusableView? {
        
        if let item = self.dataSource.itemIdentifier(for: indexPath),
            item is HasBadgeCount,
            let badgeCount = item.badgeCount {
            
            guard let badgeView = collectionView.dequeueReusableSupplementaryView(ofKind: kind, withReuseIdentifier: BadgeSupplementaryView.reuseIdentifier, for: indexPath) as? BadgeSupplementaryView else {
                fatalError("Cannot create badge supplementary")
            }
            
            badgeView.label.text = "\(badgeCount)"
            return badgeView
        } else {
            
            guard let emptyView = collectionView.dequeueReusableSupplementaryView(ofKind: kind, withReuseIdentifier: EmptySupplementaryView.reuseIdentifier, for: indexPath) as? EmptySupplementaryView else {
                fatalError("Cannot create badge supplementary")
            }
            
            return emptyView
        }
    }
}