FetchedResultsTableViewController

FetchedResultsTableViewController.swift

public class FetchedResultsTableViewController<Entity: NSFetchRequestResult, Content: View>: UITableViewController {

    private let reuseIdentifier = "FetchedResultsCell"
    private let fetchedResultsController: NSFetchedResultsController<Entity>
    private var selectionType: SelectionType = .single
    private var cellSelectionStyle: UITableViewCell.SelectionStyle = .default
    private let baseQuery: Query<Entity>
    private var cellContent: (Entity, _ isSelected: Bool) -> Content
    private var didSelectRow: ((Entity) -> Void)?
    
    public init(parentView: FetchedResultsTableViewControllerWrapper<Entity, Content>, context: NSManagedObjectContext) {
        self.cellContent = parentView.cellContent
        self.didSelectRow = parentView.didSelectRow
        self.baseQuery = parentView.query
        self.selectionType = parentView.selectionType
        self.cellSelectionStyle = parentView.cellSelectionStyle

        let entityName = String(describing: Entity.self)
        let fetchRequest: NSFetchRequest<Entity> = NSFetchRequest<Entity>(entityName: entityName)
        fetchRequest.sortDescriptors = baseQuery.sortDescriptors
        fetchRequest.predicate = baseQuerySet.predicate
        fetchRequest.fetchBatchSize = 20 // 

        self.fetchedResultsController = NSFetchedResultsController(
            fetchRequest: fetchRequest,
            managedObjectContext: context,
            sectionNameKeyPath: nil,
            cacheName: nil
        )
        super.init(style: .plain)
    }

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

    public override func viewDidLoad() {
        super.viewDidLoad()
        tableView.register(UITableViewCell.self, forCellReuseIdentifier: reuseIdentifier)
        tableView.delegate = self
        tableView.dataSource = self
        tableView.separatorStyle = .none
    }

    // MARK: - Table view data source
    override public func numberOfSections(in tableView: UITableView) -> Int {
        return fetchedResultsController.sections?.count ?? 0
    }

    override public func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
        return fetchedResultsController.sections?[section].numberOfObjects ?? 0
    }

    override public func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
        let cell = tableView.dequeueReusableCell(withIdentifier: reuseIdentifier, for: indexPath)

        /// Workaround: Clear subviews from reused cells
        /// Sometimes old cell weren't clearning out which retained in memory.
        cell.contentView.subviews.forEach { $0.removeFromSuperview() }
        cell.selectionStyle = cellSelectionStyle

        let item = fetchedResultsController.object(at: indexPath)
        let isItemSelected = selectedEntities.contains(item)
        let cellContentView = cellContent(item, isItemSelected)
        let hostingController = UIHostingController(rootView: cellContentView)
        hostingController.view.frame = cell.contentView.bounds
        hostingController.view.backgroundColor = .clear
        hostingController.view.translatesAutoresizingMaskIntoConstraints = false
        cell.contentView.addSubview(hostingController.view)
        NSLayoutConstraint.activate([
            hostingController.view.leadingAnchor.constraint(equalTo: cell.contentView.leadingAnchor),
            hostingController.view.trailingAnchor.constraint(equalTo: cell.contentView.trailingAnchor),
            hostingController.view.topAnchor.constraint(equalTo: cell.contentView.topAnchor),
            hostingController.view.bottomAnchor.constraint(equalTo: cell.contentView.bottomAnchor)
        ])
        hostingController.didMove(toParent: self)
        return cell
    }

    public override func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {
        tableView.deselectRow(at: indexPath, animated: true)
    }
    
    fileprivate func updateQueryIfNeeded(with searchText: String?) {
         // Update your search query here. 
    }     
}