I have a UITableView with a diffable datasource and for the life of me I can't seem to work out how to get headers for my sections. The sections are there, as well as the empty header cells. Bit how do I populate the headers with my custom type AnnotationType?

Related, how do I properly refactor my ViewController to have the data source ij it's own seperate class?

My enum (for the sections):

class AnnotationsController {
    enum AnnotationType: String, Codable, Hashable, CaseIterable {
        case tips, poi

        var image: UIImage {
            switch self {
            case .tips:
                return ProjectImages.annotationTypeTips
            case .poi:
                return ProjectImages.annotationTypePoi
            }
        }
    }
    (...)
}

My viewcontroller:

class AnnotationsViewController: UIViewController {
    typealias Annotation = AnnotationsController.Annotation
    typealias AnnotationType = AnnotationsController.AnnotationType

    let annotationsController = AnnotationsController(with: ProjectsController.activeProject!)

    var tableView: UITableView!
    var dataSource: UITableViewDiffableDataSource<AnnotationType, Annotation>!

    override func viewDidLoad() {
        super.viewDidLoad()

        configureViewController()
        configureTableView()
        createDataSource()
        updateData(on: annotationsController.filteredAnnotations())
        configureSearchController()
    }

    (...)

    func createDataSource() {
        dataSource = UITableViewDiffableDataSource<AnnotationType, Annotation>(tableView: tableView) { (tableView, indexPath, annotation) in
            return self.configure(AnnotationCell.self, with: annotation, for: indexPath)
        }
    }

    func updateData(on annotations: [Annotation]) {
        var snapshot = NSDiffableDataSourceSnapshot<AnnotationType, Annotation>()
        //Append available sections
        AnnotationType.allCases.forEach { snapshot.appendSections([$0]) }

        //Append annotations to their corresponding sections
        annotations.forEach { (annotation) in
            snapshot.appendItems([annotation], toSection: annotation.type as AnnotationType)
        }

        //Force the update on the main thread to silence a warning about tableview not being in the hierarchy!
        DispatchQueue.main.async {
            self.dataSource.apply(snapshot, animatingDifferences: true)
        }
    }

    ///Configure any type of cell that conforms to selfConfiguringAnnotationCell!
    func configure<T: SelfConfiguringAnnotationCell>(_ cellType: T.Type, with annotation: Annotation, for indexPath: IndexPath) -> T {
        guard let cell = tableView.dequeueReusableCell(withIdentifier: cellType.reuseIdentifier, for: indexPath) as? T else {
            fatalError("Unable to dequeue \(cellType)")
        }

        cell.configure(with: annotation)
        return cell
    }

    (...)

    private func configureViewController() {
        title = annotationsController.project.title
        view.backgroundColor = .systemPurple
        navigationController?.navigationBar.prefersLargeTitles = true
        navigationController?.navigationBar.tintColor = .systemOrange
        navigationItem.leftBarButtonItem = UIBarButtonItem(image: ProjectImages.barButtonClose, style: .plain, target: self, action: #selector(closeProject))
    }

    private func configureTableView() {
        tableView = UITableView(frame: view.bounds, style: .grouped)
        view.addSubview(tableView)
        tableView.delegate = self
        tableView.autoresizingMask = [.flexibleWidth, .flexibleHeight]
        tableView.backgroundColor = .clear

        tableView.register(AnnotationCell.self, forCellReuseIdentifier: AnnotationCell.reuseIdentifier)
    }
}

extension AnnotationsViewController: UITableViewDelegate {   
}

Any help really appreciated. I'm going blind here, staring at this thing forever ...

You need the viewForHeaderInSection method implemented. Here dequeue the header view, configure it and return it.

As for the refactor, you can create your own class that inherits from NSObject and implements the table view datasource protocol. Then create instance of this class in your VC and set it as the table view delegate.

Thanks @nemecek-filip ~~Could you help me a bit more, how do I get the correct section from my enum? My enum doesn't have an Int. I'd also like to use a custom header cell ...~~ I'm somewhat further ... 👍

//MARK: - Ext. TableViewDelegate
extension AnnotationsViewController: UITableViewDelegate {
    func tableView(_ tableView: UITableView, viewForHeaderInSection section: Int) -> UIView? {
        let annotationType = AnnotationType.allCases[section]
        let label = UILabel()
        label.text = annotationType.rawValue
        return label
    }
}

Now onto dequeing a header cell and displaying it!

You want to have different views for headers or one? Also if you plan on using only UILabel you can use the titleForHeader method instead and just return string.