Unexpectedly Found nil On TableView While Moving From ParentVC to ContainerVC

Question

Created Dec ’20

Replies 5

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I have a problem with moving from parent viewcontroller to a container viewcontroller. My container viewcontroller has a UITableView inside it and whenever I try to switch to it from the parent viewcontroller it always return nil, saying that the UITableView doesn't exist.

I know that this problem is probably related to the UITableView is not available yet during the time when I were trying to move into the container viewcontroller. I try to move the setup code into ViewWillAppear but still it doesn't help so I assume this to be a kind of problem where the UITableView is not available yet to show on the screen. Below is my code:

func showSearchAccountVC() {

print("Begin to move into SearchAccountVC")

let searchAccountVC = SearchAccountViewController()



addChild(searchAccountVC)

self.view.addSubview(searchAccountVC.view)



searchAccountVC.didMove(toParent: self)

searchAccountVC.view.frame = self.view.bounds

}

// MARK: This is in container viewcontroller
class SearchAccountViewController: UIViewController {

@IBOutlet weak var searchAccountTableView: UITableView!



override func viewDidLoad() {

super.viewDidLoad()

self.view.backgroundColor = .red

// Do any additional setup after loading the view.

//self.view.backgroundColor = .red

searchAccountTableView.separatorStyle = .none

searchAccountTableView.estimatedRowHeight = 100

searchAccountTableView.rowHeight = UITableView.automaticDimension

searchAccountTableView.delegate = self

searchAccountTableView.dataSource = self

}
}

Can someone tell me how would I solve this kind of problem? Your response will be highly appreciated!

Boost

Answer 1

Claude31 OP

Dec ’20

When you post code it is better to use "Paste and Match Style"
and the code formatter tool (<>)

Code Block     func showSearchAccountVC() {
        print("Begin to move into SearchAccountVC")
        let searchAccountVC = SearchAccountViewController()
        addChild(searchAccountVC)
        self.view.addSubview(searchAccountVC.view)
        searchAccountVC.didMove(toParent: self)
        searchAccountVC.view.frame = self.view.bounds
    }
// MARK: This is in container viewcontroller
class SearchAccountViewController: UIViewController {
    @IBOutlet weak var searchAccountTableView: UITableView!
    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view.
        searchAccountTableView.delegate = self	// Do it earlier
        searchAccountTableView.dataSource = self
        self.view.backgroundColor = .red
        searchAccountTableView.separatorStyle = .none
        searchAccountTableView.estimatedRowHeight = 100
        searchAccountTableView.rowHeight = UITableView.automaticDimension
        //	searchAccountTableView.delegate = self
        // searchAccountTableView.dataSource = self
    }
}

Which line is the crash ? line 24 ?
Did you connect searchAccountTableView to the tableview in Interface Builder (control-drag from the dot to the tableView)

I have a problem with moving from parent viewcontroller to a container viewcontroller. My container viewcontroller has a UITableView inside it

Who is parent ViewController ?
Who is the container viewcontroller ? Is it SearchAccountViewController ?

whenever I try to switch to it from the parent viewcontroller it always return nil, saying that the UITableView doesn't exist.

How do you "switch"
Where is it in code ?

I would also advise to move delegate assignment sooner.

0

Answer 2

OOPer OP

Dec ’20

The worst part of your code is this line:

Code Block         let searchAccountVC = SearchAccountViewController()

Generally, instantiating a view controller with init() always a bad option in almost all cases.
If you want to make @IBOutlets or all other views constructed on the storyboard work, you need to instantiate a view controller through the storyboard.

Code Block         guard let searchAccountVC = self.storyboard?.instantiateViewController(identifier: "SearchAccountViewController") as? SearchAccountViewController else {
            print("Something wrong in storyboard")
            return
        }

(You need to put Storyboard ID as SearchAccountViewController in your storyboard, when you want to use this code.)

One more, why don't you use present(_:animation:complete:) to show SearchAccountViewController?

Code Block     func showSearchAccountVC() {
        print("Begin to move into SearchAccountVC")
        guard let searchAccountVC = self.storyboard?.instantiateViewController(identifier: "SearchAccountViewController") as? SearchAccountViewController else {
            print("Something wrong in storyboard")
            return
        }
        searchAccountVC.modalPresentationStyle = .fullScreen //Change this as you like
        self.present(searchAccountVC, animated: true, completion: nil)
    }

If you really want to implement so called ContainerVC, you should be define a Container View on your storyboard.
With using Container View, you are not worried with instantiating a VC. You just need to hide and show your Container View.

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Answer 3

imdavid1007@gmail.com OP

Dec ’20

@Claude31

Yes, line 24 got crash when I try to switch from my parent viewcontroller.
parent ViewController is SearchViewController while the child viewcontroller is SearchAccountViewController. I try to switch to the child ViewController whenever user tap on a UISearchBar.
I switch using:

Code Block   class SearchViewController: UIViewController {
	 func showSearchAccountVC() {        
			print("Begin to move into SearchAccountVC")        
			let searchAccountVC = SearchAccountViewController()        
			addChild(searchAccountVC)        
			self.view.addSubview(searchAccountVC.view)        
			searchAccountVC.didMove(toParent: self)       
			searchAccountVC.view.frame = self.view.bounds
	 }
}

This is a delegate method from a UITableViewCell class which will trigger whenever user tap on a UISearchBar.

To sum up the problem, tableView is perfectly connected to the ViewController but whenever I try to switch to it from the parent ViewController, Xcode give me the "Unexpected Found nil" message saying that the tableviw is nil.

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Answer 4

imdavid1007@gmail.com OP

Dec ’20

@OOPer

I guess I am thinking wrong on using container viewcontroller, I think I suppose show a new viewcontroller on top of another viewcontroller instead of using a container viewcontroller.

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Answer 5

OOPer OP

Dec ’20

I think I suppose show a new viewcontroller on top of another viewcontroller instead of using a container viewcontroller.

Thanks for replying to my comment. Please tell us how you have made it when you successfully implement what you want.

0