SwiftUI wrapper for UICollectionView

CollectionView.swift

import UIKit
import SwiftUI

public protocol SectionProtocol: Hashable {
    associatedtype Item: Hashable
  
    var items: [Item] { get }
}

extension CollectionView {
    public typealias DataSource = UICollectionViewDiffableDataSource<Section, Item>
    public typealias SnapShot = NSDiffableDataSourceSnapshot<Section, Item>

    public typealias CellProvider = DataSource.CellProvider
    public typealias SupplementaryViewProvider =
        (SnapShot, UICollectionView, String, IndexPath) -> UICollectionReusableView?

    public typealias CollectionViewProvider = () -> UICollectionView
    public typealias CollectionViewUpdateCompleteHandler = (UICollectionView) -> Void
}

public struct CollectionView<Section, Item>
    where
    Section: SectionProtocol,
    Section.Item == Item {

    private let collectionViewProvider: CollectionViewProvider
    private let cellProvider: CellProvider
    private let supplementaryViewProvider: SupplementaryViewProvider?
    private let updateCompleteHandler: CollectionViewUpdateCompleteHandler?

    private var animateCollectionUpdates: Bool = true

    private let sections: [Section]

    public init(sections: [Section],
                collectionViewProvider: @escaping  CollectionViewProvider,
                cellProvider: @escaping CellProvider,
                supplementaryViewProvider: SupplementaryViewProvider? = nil,
                updateCompleteHandler: CollectionViewUpdateCompleteHandler? = nil) {

        self.collectionViewProvider = collectionViewProvider
        self.cellProvider = cellProvider
        self.sections = sections
        self.supplementaryViewProvider = supplementaryViewProvider
        self.updateCompleteHandler = updateCompleteHandler
    }
}

extension CollectionView: UIViewRepresentable {
    public func makeCoordinator() -> Coordinator {
        Coordinator()
    }

    public func makeUIView(context: UIViewRepresentableContext<CollectionView>) -> UICollectionView {
        let collectionView = collectionViewProvider()
        let datasource = DataSource(collectionView: collectionView,
                                    cellProvider: cellProvider)
        datasource.setSupplementaryViewProvider(with: supplementaryViewProvider)
        context.coordinator.datasource = datasource
        return collectionView
    }

    public func updateUIView(_ uiView: UICollectionView,
                             context: UIViewRepresentableContext<CollectionView>) {

        context.coordinator.applySnapshotInBackground(sections: sections,
                                                      animated: animateCollectionUpdates) {
            updateCompleteHandler?(uiView)
        }
    }
}

extension UICollectionViewDiffableDataSource where SectionIdentifierType: SectionProtocol,
                                                   SectionIdentifierType.Item == ItemIdentifierType {
    func setSupplementaryViewProvider(
        with provider: CollectionView<SectionIdentifierType, ItemIdentifierType>.SupplementaryViewProvider?) {

        guard let provider = provider else {
            supplementaryViewProvider = nil
            return
        }

        supplementaryViewProvider = { [weak self] (collecion, kind, idx) in
            guard let self = self else {
                return nil
            }

            return provider(self.snapshot(), collecion, kind, idx)
        }
    }
}

public extension CollectionView {
    func animatingDifferences(_ animated: Bool) -> Self {
        var selfCopy = self
        selfCopy.animateCollectionUpdates = animated
        return selfCopy
    }
}

CollectionViewCoordinator.swift

import UIKit
import SwiftUI

extension CollectionView {
    public class Coordinator: NSObject {
        var datasource: DataSource?

        private let updateQueue = DispatchQueue(
            label: "CollectionView.Coordinator.Update.Queue",
            qos: .userInteractive)

        func applySnapshotInBackground(sections: [Section],
                                       animated: Bool,
                                       complete: @escaping () -> Void) {

            updateQueue.async { [weak self] in
                guard let self = self else {
                    DispatchQueue.main.async {
                        complete()
                    }
                    return
                }

                self.applySnapshot(sections: sections, animated: animated) {
                    DispatchQueue.main.async {
                        complete()
                    }
                }
            }
        }
    }
}

extension CollectionView.Coordinator {
    private func applySnapshot(sections: [Section],
                               animated: Bool,
                               complete: @escaping () -> Void) {

        guard let datasource = self.datasource else {
            complete()
            return
        }

        var snapshot = CollectionView.SnapShot()

        snapshot.appendSections(sections)
        sections.forEach {
            snapshot.appendItems($0.items, toSection: $0)
        }

        datasource.apply(snapshot, animatingDifferences: animated) {
            complete()
        }
    }
}

HostingCollectionViewCell.swift

public protocol ReusableView {

}

public extension ReusableView {
    static var reuseIdentifier: String {
       "\(self)"
    }
}

public class HostingCollectionViewCell<Content: View>: UICollectionViewCell
    where Content: ReusableView {

    private var hostingController: UIHostingController<Content>?
    
    override init(frame: CGRect) {
        super.init(frame: frame)
    }

    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
    
    public static var reuseIdentifier: String {
        String(describing: Content.reuseIdentifier)
    }
    
    public func set(rootView: Content) {
        guard let host = hostingController else {
            let host = UIHostingController(rootView: rootView)

            let parentController = resolveParentViewController()
            parentController?.addChild(host)

            addSubview(host.view)
            host.view.translatesAutoresizingMaskIntoConstraints = false

            NSLayoutConstraint.activate([
                leadingAnchor.constraint(equalTo: host.view.leadingAnchor),
                trailingAnchor.constraint(equalTo: host.view.trailingAnchor),
                topAnchor.constraint(equalTo: host.view.topAnchor),
                bottomAnchor.constraint(equalTo: host.view.bottomAnchor)
            ])

            parentController.map { host.didMove(toParent: $0) }
            return
        }

        host.rootView = rootView
        host.view.invalidateIntrinsicContentSize()
    }

    deinit {
        hostingController?.willMove(toParent: nil)
        hostingController?.view.removeFromSuperview()
        hostingController?.removeFromParent()
        hostingController = nil
    }
}

fileprivate extension UIView {
    func resolveParentViewController() -> UIViewController? {
        var parentResponder: UIResponder? = self
        while parentResponder != nil {
            parentResponder = parentResponder?.next
            if let viewController = parentResponder as? UIViewController {
                return viewController
            }
        }
        return nil
    }
}

@KazaiMazai - I have been using your updated implementation of CollectionView and I am running into some issues. 1) The functions CollectionView.animateDifferences(...), .onUpdate(...), and .collectionViewDelegate(...) need to return selfCopy rather than self. 2) The UICollectionViewDelegate is held as a weak reference and is therefore nil upon returning from CollectionView.makeUIView(...). I have worked around these issues by modifying your code specifically for my use (not a general solution). If you would like to resolve the issues, I would be happy to give you feedback on the fix. Thanks for your efforts.

@KazaiMazai - I have been using your updated implementation of CollectionView and I am running into some issues. 1) The functions CollectionView.animateDifferences(...), .onUpdate(...), and .collectionViewDelegate(...) need to return selfCopy rather than self. 2) The UICollectionViewDelegate is held as a weak reference and is therefore nil upon returning from CollectionView.makeUIView(...). I have worked around these issues by modifying your code specifically for my use (not a general solution). If you would like to resolve the issues, I would be happy to give you feedback on the fix. Thanks for your efforts.

@jafienberg
Hey! Just noticed you reply that I missed a year ago. Thanks for pointing it out. Fixed the issues in the latest revision.