swift call a func from another viewcontroller

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")
}