swift call a func from another viewcontroller - swift

Question

I would like to call a func from another viewcontroller.
here with the code in pubListViewController: It is working fine.
override func viewDidAppear(_ animated: Bool) {
navigationBarTitleImage(imageTitle: "IconTitle")
}
func navigationBarTitleImage(imageTitle: String) {
// 1
// let nav = self.navigationController?.navigationBar
// 2
// nav?.barStyle = UIBarStyle.black
// nav?.tintColor = UIColor.yellow
// 3
let imageView = UIImageView(frame: CGRect(x: 0, y: 0, width: 10, height: 10))
imageView.contentMode = .scaleAspectFit
// 4
let image = UIImage(named: imageTitle)
imageView.image = image
// 5
navigationItem.titleView = imageView
}
now I try to call it in another viewcontroller as below, but it shows nothing.
override func viewDidAppear(_ animated: Bool) {
pubListViewController().navigationBarTitleImage(imageTitle: "addTitle")
}

Answer 1

When you're using notation like that pubListViewController() you call free empty initializer of pubListViewController which creates new instance of class pubListViewController, but you do already have one in your screens flow I bet, so all changes made by function you're calling later are being applied to invisible instance of pubListViewController.
To solve this problem you need a reference actually displaying instance of pubListViewController from your another viewcontroller
In another viewcontroller you can create a property of type pubListViewController, then before showing another viewcontroller set its property to self, and use that property from wherever you want in another viewcontroller.
class PubListViewController: UIViewController {
func prepareForSegue(/**/){ // actually do that in the place where you showing your another viewcontroller, I don't know if you're using segues or not
destinationViewController.parentPubListViewController = self
}
}
class AnotherViewController: UIViewController {
// declare property (weak and optional to avoid crashes or memory leaks if you forget to set that property from parent view controller
weak var parentPubListViewController: PubListViewController?
// use it anywhere you need
parentPubListViewController?.navigationBarTitleImage(imageTitle: "addTitle")
}