新世代のUITableViewController：DiffableDataSource + 検索機能

最終効果：

検索欄で検索文字を入力する時表示内容は動的に変更する。

Memo

struct Memo: Hashable {
    var id = UUID().uuidString
    var title = ""
    var detail = ""
    var editTime = Date()
    
    func hash(into hasher: inout Hasher) {
        hasher.combine(id)
    }
}

MemoListTableViewController

class MemoListTableViewController: UITableViewController {
    enum Section {
        case main
    }
    
    let cellReuseIdentifier = "memo"
    
    var list = [Memo]()
    var dataSource: UITableViewDiffableDataSource<Section, Memo>!

    override func viewDidLoad() {
        super.viewDidLoad()

        // debug data
        for i in 1...10 {
            var memo = Memo()
            memo.title = "Memo\(i)"
            memo.detail = "南无阿弥陀佛南无阿弥陀佛南无阿弥陀佛南无阿弥陀佛南无阿弥陀佛南无阿弥陀佛南无阿弥陀佛南无阿弥陀佛南无阿弥陀佛"
            list.append(memo)
        }
        
        // configure data source
        dataSource = UITableViewDiffableDataSource(tableView: tableView, cellProvider: { [unowned self] (tableView, indexPath, memo) -> UITableViewCell? in
            let cell = tableView.dequeueReusableCell(withIdentifier: self.cellReuseIdentifier, for: indexPath)
            cell.textLabel?.text = memo.title
            
            let formatter = DateFormatter()
            formatter.dateStyle = .short
            cell.detailTextLabel?.text = formatter.string(from: memo.editTime) + " " + memo.detail
            
            return cell
        })
        
        update(with: list)
        
        // configure search controller
        let searchController = UISearchController()
        searchController.searchResultsUpdater = self
        searchController.obscuresBackgroundDuringPresentation = false
        navigationItem.searchController = searchController
    }
    
    override func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {
        guard let memo = dataSource.itemIdentifier(for: indexPath) else { return }
        
        let detailVC = storyboard?.instantiateViewController(withIdentifier: "detail") as! MemoDetailViewController
        detailVC.memo = memo
        navigationController?.pushViewController(detailVC, animated: true)
    }
    
    private func update(with list: [Memo]) {
        var snapshot = NSDiffableDataSourceSnapshot<Section, Memo>()
        snapshot.appendSections([.main])
        snapshot.appendItems(list, toSection: .main)
        dataSource.apply(snapshot)
    }
}

extension MemoListTableViewController: UISearchResultsUpdating {
    func updateSearchResults(for searchController: UISearchController) {
        guard let filter = searchController.searchBar.text, !filter.isEmpty else {
            update(with: list)
            return
        }
        
        let lowerCasedFilter = filter.lowercased()
        let filteredList = list.filter { (memo) -> Bool in
            memo.title.lowercased().contains(lowerCasedFilter) || memo.detail.contains(lowerCasedFilter)
        }
        
        update(with: filteredList)
    }
}