ScrollView IBOutlet nil when using protocol to call function in viewDidDisappear - swift

Question

I have a scrollView that contains a dynamic amount of WeatherViewControllers each displaying the weather data of a different city the user has saved. The user can segue from the WeatherViewControllers to a CityListViewController. Where they can add and remove cities from their list which in turn should add and remove WeatherViewControllers from the scrollView upon dismissing the CityListViewController, this is where I am running into a problem.
Currently I am trying to use a protocol in to call the func reloadScrollView which calls viewDidLoad in the scrollViewController upon dismissing(viewDidDisappear) the CityListViewController but am getting an error:
Fatal error: Unexpectedly found nil while unwrapping an Optional value: file
when it gets to:
totalScrollView.addSubview(weatherScreen.view)
Using debugger I have found that totalScrollView is nil and that is causing the problem. Is there a way to make the scrollView load so it is not nil when dismissing the other viewController
OR
is the a better time to call use this protocol to call this function?
Side Note: Upon initially opening the app the scrollView loads properly with all the correct WeatherViewControllers in the UIScrollView and the correct cities in the list.
class ScrollViewController: UIViewController, ScrollReloadProtocol {
func reloadScrollView() {
print("SCROLL RELOADED!!!!!*******")
self.viewDidLoad()
}
#IBOutlet var totalScrollView: UIScrollView!
var pages = [ViewController]()
var x = 0
var weatherScreensArray = [SavedCityEntity]()
var weatherScreenStringArray = [String]()
let context = (UIApplication.shared.delegate as! AppDelegate).persistentContainer.viewContext
var horizString = "H:|[page1(==view)]"
let defaults = UserDefaults.standard
override func viewDidLoad() {
super.viewDidLoad()
//userDefaults used to keep track of which screen is which to put different cities on different viewControllers
defaults.set(0, forKey: "screenNumber")
//load cities to get number of cities saved
loadCities()
var views : [String: UIView] = ["view": view]
//create all weatherWeatherControllers
while x <= weatherScreensArray.count {
pages.append(createAndAddWeatherScreen(number: x))
weatherScreenStringArray.append("page\(x+1)")
views["\(weatherScreenStringArray[x])"] = pages[x].view
let addToHoriz = "[\(weatherScreenStringArray[x])(==view)]"
horizString.append(addToHoriz)
x+=1
}
horizString.append("|")
let verticalConstraints = NSLayoutConstraint.constraints(withVisualFormat: "V:|[page1(==view)]|", options: [], metrics: nil, views: views)
let horizontalConstraints = NSLayoutConstraint.constraints(withVisualFormat: horizString, options: [.alignAllTop, .alignAllBottom], metrics: nil, views: views)
NSLayoutConstraint.activate(verticalConstraints + horizontalConstraints)
}
//Function to create and add weatherViewController
func createAndAddWeatherScreen(number: Int) -> ViewController {
defaults.set(number, forKey: "screenNumber")
let story = UIStoryboard(name: "Main", bundle: nil)
let weatherScreen = story.instantiateViewController(identifier: "View Controller") as! ViewController
weatherScreen.view.translatesAutoresizingMaskIntoConstraints = false
totalScrollView.addSubview(weatherScreen.view)
addChild(weatherScreen)
weatherScreen.didMove(toParent: self)
return weatherScreen
}
}

Answer 1

Skipping that fact that your are not doing it right, let's forcus on the one issue at a time. You are trying to access the totalScrollView implicitly in the viewDidLoad where if the outlet is linked it should be loaded at that point. If it is nil you should:
Make sure that you have the .storyboard or .xib file defining the ScrollViewController layout.
Make sure you are loading this controller from that storyboard/xib.
Make sure that the view controller in the storyboard/xib file has set its class to ScrollViewController, similar to the following print screen:
Make sure that the outlet is linked in the storyboard/xib to this property in your code file (probably ScrollViewController.swift). If not:
open storyboard and sorucecode file in separate editors
drag and drop from the dot on the left of the property declaration to the UIScrollView in the storyboard
make sure that there is added a link to Referencing Outlets