OpenClosePrinciple.swift

protocol ViewModelDelegate {
    func dataLoaded();
}

class ViewModel {
    var objects: [Object]?
    var delegate: ViewModelDelegate?

    func getObjects() {
        // .. do something fancy in background here
        self.objects = objects
        delegate?.dataLoaded();
    }
}

class ViewController: UITableViewController, ViewModelDelegate {
    func viewDidLoad() {
        viewModel.delegate = self;
        viewModel.getObjects();
    }

    func dataLoaded() {
        self.tableView.reloadData();
    }

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

        let data = viewModel.objects[IndexPath.row]
        cell.setup(data: data)
        return cell
    }
}