Items in function become nil when function is called - Swift 3 - ios

Question

I have a custom class segmented control that is communicating with a view controller every time a different item in the segmented control is selected. I'm able to pass data to the view controller just fine.
#IBDesignable class SegmentedControlLeft: UIControl {
var selectedIndex: Int = 0 {
didSet {
displayNewSelectedIndex()
let storyboard = UIStoryboard(name: "Main", bundle: nil)
let messagesViewController: MessagesViewController = storyboard.instantiateViewController(withIdentifier: "PurpleVC") as! MessagesViewController
messagesViewController.animateViews(selectedIndex: selectedIndex)
}
}
...some more code
}
However, when I try to use some basic logic every time the passed variable is updated, all the items inside the "animateViews" function apparently turn nil. I receive the infamous "unexpectedly found nil" error. This only happens when i try to use the variable I'm passing, everything runs as expected otherwise outside of the function.
import UIKit
class MessagesViewController: UIViewController, UITableViewDelegate, UITableViewDataSource, UICollectionViewDelegate, UICollectionViewDataSource, UICollectionViewDelegateFlowLayout {
#IBOutlet weak var messageTableView: UITableView!
#IBOutlet weak var boostCollectionView: UICollectionView!
override func viewDidLoad() {
super.viewDidLoad()
...all cells, delegates, and datasource are registered and setup in here.
}
func animateViews(selectedIndex: Int) {
if selectedIndex == 0 {
print("LEFT") // prints as expected
self.messagesTableView.isHidden = false // unexpected found nil error on each of these items.
self.boostCollectionView.isHidden = true
} else if selectedIndex == 1 {
print("RIGHT") // prints correctly when updated
self.messageTableView.isHidden = true
self.boostCollectionView.isHidden = false
}
}
}
I've been playing around with this for far too long, how do I get views in the animateViews function to hide and unhide using the variable I'm passing from the segmented Control?
There is probably an amazingly simple fix that I'm not getting here, but I appreciate you for getting your eyeballs this far. Thank you!

Answer 1

This is happening because by the time you call
messagesViewController.animateViews(selectedIndex: selectedIndex), the MessagesViewController is not instantiated. That also means that the Table view and Collection View are not drawn yet and you are trying to use it before it is being created.
The viewDidLoad() method has to be called once to use the UI Elements of the View Controller.
Each time this line is called let messagesViewController: MessagesViewController = storyboard.instantiateViewControl, a new instance of the view controller is created.
Suggestion:
My suggestion will be to create an outlet of the segmented controls(seems like you are having multiple Segmented Controls in View Controller), and create a method like #IBAction func indexChanged(_ sender: AnyObject) { and assign this action to the value changed property of the segmented controls.
You can differentiate among the segmented controls using the sender parameter.