TableView inside a CollectionView crashes the app - swift

Question

I am building a multi screen app which uses a UICollection view to navigate between UIViewControllers. The left one is green and the right is red. Swiping left or right brings you to the ViewController. It works, but when I add a TableViewController to the green one, the app crashes. I added all outlets. It says:
SwipeViewController[11639:3937203] Fatal error: Unexpectedly found nil while implicitly unwrapping an Optional value: file SwipeViewController/GreenViewController.swift, line 21
which points to tableViewI.delegate = self.
Here is the CollectionView code:
class ViewController: UIViewController, UICollectionViewDelegate, UICollectionViewDelegateFlowLayout, UICollectionViewDataSource {
#IBOutlet var collectionView: UICollectionView!
override func viewDidLoad() {
super.viewDidLoad()
collectionView.backgroundColor = .yellow
collectionView.register(UICollectionViewCell.self, forCellWithReuseIdentifier: "collectionViewCell")
collectionView.isPagingEnabled = true
collectionView.scrollToItem(at: IndexPath(item: 1, section: 0), at: .centeredVertically, animated: false)
}
func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, minimumLineSpacingForSectionAt section: Int) -> CGFloat {
return 0
}
func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
return 2
}
func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "collectionViewCell", for: indexPath)
//cell.backgroundColor = indexPath.item % 2 == 0 ? .purple : cell.backgroundColor
switch indexPath.row {
case 0:
self.addChild(GreenViewController())
cell.contentView.addSubview(GreenViewController().view)
case 1:
self.addChild(RedViewController())
cell.contentView.addSubview(RedViewController().view)
default:
print("nothing")
}
return cell
}
func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {
return CGSize(width: self.view.frame.width, height: self.view.frame.height)
}
And here the green ViewController containing the tableView:
class GreenViewController: UIViewController, UITableViewDelegate, UITableViewDataSource {
#IBOutlet weak var tableViewI: UITableView!
override func viewDidLoad() {
super.viewDidLoad()
self.view.backgroundColor = .green
tableViewI.delegate = self
tableViewI.dataSource = self
tableViewI.register(UINib.init(nibName: "cellID", bundle: nil), forCellReuseIdentifier: "cellID")
}
func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
let cell = tableView.dequeueReusableCell(withIdentifier: "cellID") as! TableViewCell
cell.backgroundColor = .blue
return cell
}
func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
return 1
}

Answer 1

The problem is how you are creating the object of GreenViewController class.
You must load it from the storyboard instead of just creating it from the init method of GreenViewController. Otherwise, outlet properties will be nil.
let vc = storyboard?.instantiateViewController(withIdentifier: "yourIdentifier") as! GreenViewController

Answer 2

I think the problem is in reference to GreenViewController
try to save viewController as property before adding it as a child.
possible problem is that your greenViewController could be deallocated before you access it.
let greenViewController = GreenViewController()
let redViewController = RedViewController()
func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "collectionViewCell", for: indexPath)
//cell.backgroundColor = indexPath.item % 2 == 0 ? .purple : cell.backgroundColor
switch indexPath.row {
case 0:
self.addChild(greenViewController)
cell.contentView.addSubview(greenViewController.view)
case 1:
self.addChild(redViewController)
cell.contentView.addSubview(redViewController.view)
default:
print("nothing")
}
return cell
}