Swift：UIlabel 文本属性已更改，但 UI 中的显示值未更改

Question

When a user clicks on a collection view item, I want to change the UILabelView text property:

// This is another viewController not the one containing the label
// Handle collectionViewItem selection
func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
    print("INSIDE TableViewCell2.collectionView 3")
    TabsBarController.sharedInstance.testTitle = "UILabelText"
    print("didSelectItem\(indexPath)")
}

Once it's set, I try to update it here:

  class TabsBarController: UIViewController {
    static let sharedInstance = TabsBarController()
    var movieTitle:  UILabel? = UILabel(frame: CGRect(x: 0, y: 0, width: 300.00, height: 30.00));
    var testTitle: String? = nil {
        didSet {
            print("testTitle.didSet: ",testTitle!) // logs the correct text
            movieTitle?.text = testTitle
            print(" movieTitle?.text : ", movieTitle?.text ) // logs the correct text
        }
    }
}

The problem here is that even though movieTitle?.text , in the UI, the movieTitle UILabel doesn't change. I've read many answers to similar question, and all of them point to using the main thread, so I added this:

 class TabsBarController: UIViewController {
        static let sharedInstance = TabsBarController()
        var movieTitle:  UILabel? = UILabel(frame: CGRect(x: 0, y: 0, width: 300.00, height: 30.00));
        var testTitle: String? = nil {
            didSet {
                // I added this but still nothing changed.
                DispatchQueue.main.async {
                    // Run UI Updates
                    print("testTitle.didSet: ",testTitle!) // logs the correct text
                    movieTitle?.text = testTitle
                    print(" movieTitle?.text : ", movieTitle?.text ) // logs the correct text
                }
                
            }
        }
    }

But, still the UI doesn't get updated. Any idea why is this happening and how to solve it?

NOTE: This is the hierarchy :
The hierarchy is like this TabsBarViewController-> MoviesViewController -> UITableView->UitableViewCell->CollectionView

Answer 1

Based on the project hierarchy, I had to follow the instructions here in order to be able to access the UITabsBarController testTitle property from inside the tableViewCell . Just one caveat, I had to do this casting:

 // Handle collectionViewItem selection
    func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
        print("INSIDE TableViewCell2.collectionView 3")
   
          if let vc2 =  self.viewController?.parent as? TabsBarController {
             vc2.testTitle = "THIS WILL DEFINITELY ABSOLUTELY WORK I DONT CARE"
        }
        print("didSelectItem\(indexPath)")
    }