Unexpected nil after adding programmatic view instead of storyboard

Question

I have an application written in the MVVM-C pattern, using RxSwift

After adding a new view programmatically, the application crashes with a

Thread 1: Fatal error: Unexpectedly found nil while unwrapping an Optional value

error. I am at a complete loss, the implementation is almost exactly the same, minus the fact one view controller is a storyboard and one is not.

This is my new ViewController

import UIKit
import RxSwift
import RxCocoa

final class FeedViewController: TableViewController, ViewModelAttaching {

    var viewModel: Attachable<FeedViewModel>!
    var bindings: FeedViewModel.Bindings {
        let viewWillAppear = rx.sentMessage(#selector(UIViewController.viewWillAppear(_:)))
            .mapToVoid()
            .asDriverOnErrorJustComplete()

        let refresh = tableView.refreshControl!.rx
            .controlEvent(.valueChanged)
            .asDriver()

        return FeedViewModel.Bindings(
            fetchTrigger: Driver.merge(viewWillAppear, refresh),
            selection: tableView.rx.itemSelected.asDriver()
        )
    }

    override func viewDidLoad() {
        super.viewDidLoad()
    }

    func bind(viewModel: FeedViewModel) -> FeedViewModel {
        viewModel.posts
            .drive(tableView.rx.items(cellIdentifier: FeedTableViewCell.reuseID, cellType: FeedTableViewCell.self)) { _, viewModel, cell in
                cell.bind(to: viewModel)
            }
            .disposed(by: disposeBag)

        viewModel.fetching
            .drive(tableView.refreshControl!.rx.isRefreshing)
            .disposed(by: disposeBag)

        viewModel.errors
            .delay(0.1)
            .map { $0.localizedDescription }
            .drive(errorAlert)
            .disposed(by: disposeBag)

        return viewModel
    }

}

This is an existing one, that works but uses storyboards

final class PostsListViewController: TableViewController, ViewModelAttaching {

    var viewModel: Attachable<PostsListViewModel>!
    var bindings: PostsListViewModel.Bindings {
        let viewWillAppear = rx.sentMessage(#selector(UIViewController.viewWillAppear(_:)))
            .mapToVoid()
            .asDriverOnErrorJustComplete()
        let refresh = tableView.refreshControl!.rx
            .controlEvent(.valueChanged)
            .asDriver()

        return PostsListViewModel.Bindings(
            fetchTrigger: Driver.merge(viewWillAppear, refresh),
            selection: tableView.rx.itemSelected.asDriver()
        )
    }

    // MARK: - Lifecycle

    override func viewDidLoad() {
        super.viewDidLoad()
        setupView()
    }

    // MARK: - View Methods

    private func setupView() {
        title = "Posts"
    }

    func bind(viewModel: PostsListViewModel) -> PostsListViewModel {
        viewModel.posts
            .drive(tableView.rx.items(cellIdentifier: PostTableViewCell.reuseID, cellType: PostTableViewCell.self)) { _, viewModel, cell in
                cell.bind(to: viewModel)
            }
            .disposed(by: disposeBag)

        viewModel.fetching
            .drive(tableView.refreshControl!.rx.isRefreshing)
            .disposed(by: disposeBag)

        viewModel.errors
            .delay(0.1)
            .map { $0.localizedDescription }
            .drive(errorAlert)
            .disposed(by: disposeBag)

        return viewModel
    }

}

They are basically exactly the same. The exception is thrown on the let refresh = tableView.refreshControl!.rx line.

The working coordinator, using a Storyboard is

import RxSwift

class PostsCoordinator: BaseCoordinator<Void> {
    typealias Dependencies = HasPostService

    private let navigationController: UINavigationController
    private let dependencies: Dependencies

    init(navigationController: UINavigationController, dependencies: Dependencies) {
        self.navigationController = navigationController
        self.dependencies = dependencies
    }

    override func start() -> Observable<Void> {
        let viewController = PostsListViewController.instance()
        navigationController.viewControllers = [viewController]

        let avm: Attachable<PostsListViewModel> = .detached(dependencies)
        let viewModel = viewController.attach(wrapper: avm)

        viewModel.selectedPost
            .drive(onNext: { [weak self] selection in
                self?.showDetailView(with: selection)
            })
            .disposed(by: viewController.disposeBag)

        // View will never be dismissed
        return Observable.never()
    }

    private func showDetailView(with post: Post) {
        let viewController = PostDetailViewController.instance()
        viewController.viewModel = PostDetailViewModel(post: post)
        navigationController.showDetailViewController(viewController, sender: nil)
    }

}

I have an extension to allow me to instantiate it also

protocol Reusable {
    static var reuseID: String { get }
}

extension Reusable {
    static var reuseID: String {
        return String(describing: self)
    }
}

// MARK: - View Controller

extension UIViewController: Reusable {
    class func instance() -> Self {
        let storyboard = UIStoryboard(name: reuseID, bundle: nil)
        return storyboard.instantiateViewController()
    }
}

extension UIStoryboard {
    func instantiateViewController<T: UIViewController>() -> T {
        guard let viewController = self.instantiateViewController(withIdentifier: T.reuseID) as? T else {
            fatalError("Unable to instantiate view controller: \(T.self)")
        }
        return viewController
    }
}

The 'broken' coordinator is exactly the same, except I swapped

 let viewController = PostsListViewController.instance()

for

let viewController = FeedViewController()

I am at a complete loss at to why this is throwing. Print statements and breakpoints at various points haven't turned up a nil on any values.

Please let me know if it would be easier to share a sample app as I appreciate the code snippets may not be the most obvious.

Answer 1

The default value of the refreshControl property is nil. You need to instantiate and assign a UIRefreshControl to self.refreshControl before it exists.

When you create your view using a Storyboard and enable it, this is taken care of behind the scenes for you. Programmatically you will be required to implement this yourself.