Swift Call Particular function from another class for Present ViewController - swift

Question

My Scenario, I am trying to call a ViewController class file particular function from another one class file. Here, I am getting below warning and ViewController not presenting.
My Code Below ViewControllerA
func previewview(){ // Inside ViewControllerA
DispatchQueue.main.async {
let storyboard = UIStoryboard(name: "Main", bundle: nil)
let fileViewController = storyboard.instantiateViewController(withIdentifier: "fileviewcontroller")
let navController = UINavigationController(rootViewController: fileViewController)
self.present(navController, animated: true, completion: nil)
} }
Below code In Another Class File
import UIKit
class FileController {
//MARK:- Call a file preview
ViewControllerA().self.previewview()
}
Warning: Attempt to present on
whose view is not in the window
hierarchy!

Answer 1

Try this
Viewcontroller().FuncName()
Example:
LoginViewController().checkLoginValidation()

Answer 2

Use swift's Delegate Protocol to call a function in a class from different class.
Here is a link for understanding how delegate protocol works.
https://medium.com/#nimjea/delegation-pattern-in-swift-4-2-f6aca61f4bf5

Answer 3

Here is how you can proceed. This is just an example. You can take the idea and implement in you code as per your requirement.
Instead of creating a separate ViewController, create a ViewModel that handles the implementation of saving the file, i.e.
class SaveOptionsViewModel {
func save(file: String, handler: (()->())?) { //add parameters to save a file as per requirement
//save the file here...
handler?()
}
}
Now, in the controller that contains multiple save options, create a property of type SaveOptionsViewModel.
And present PreviewVC from SaveOptionsVC in the handler once the file is saved using the SaveOptionsViewModel after tapping the saveButton.
class SaveOptionsVC: UIViewController {
let viewModel = SaveOptionsViewModel()
#IBAction func onTapSaveButton(_ sender: UIButton) {
self.viewModel.save(file: "") {
if let previewVC = self.storyboard?.instantiateViewController(withIdentifier: "PreviewVC") {
self.present(previewVC, animated: true, completion: nil)
}
}
}
}
Add the custom implementation of PreviewVC as per your requirement.
class PreviewVC: UIViewController {
override func viewDidLoad() {
super.viewDidLoad()
}
//add the code...
}