Unexpected nil after adding programmatic view instead of storyboard - ios

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

tableView.refreshControl is nil. You are trying to force access the nil refreshControl.
The Refreshing property is Enabled for the UITableViewController in your storyboard that works. In the programmatic version, the refreshControl is not created automatically.

Answer 2

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.