Swift Small to Large Nav Bar Title Jumpy Transition - swift

Question

So on my first vc I have set the nav bar to a large title. Then I have a button which goes to a vc with a nav bar with a small title.
When I go back from my second vc to the first, it displays the small title for a bit then jumps down to the large title.
Here is my code in the first vc bc its a tab view controller:
override func viewWillAppear(_ animated: Bool) {
self.navigationController?.navigationBar.prefersLargeTitles = true
}
Here is the code for the second vc in the viewDidLoad():
self.navigationController?.navigationBar.titleTextAttributes = [NSAttributedString.Key.font: UIFont(name: "Avenir-Black", size: 20)!]
self.navigationController?.navigationBar.prefersLargeTitles = false
This is what I mean about the jumpy transition
Thanks

Answer 1

On your second ViewController Try changing the NavBarPreference inside viewWillDisappear function.
Example:
func viewWillDisappear(_ animated: Bool){
self.navigationController?.navigationBar.prefersLargeTitles = true
}
So before going back to the first vc you change the NavBar preference first
Alternative Solution: Using Storyboard
You can click on the desired VC then click on its navBarItem then go to your right to properties and on Large Title Select Never, Always or Automatic from the dropdown list.
Example

Answer 2

Short answer is to not rely on largeTitleDisplayMode = .automatic (the default value) and prefersLargeTitles = true/false but instead to be explicitly setting .always or .never with prefersLargeTitles = true (yes even when using never).
You need to always have prefersLargeTitles to be true because of this from Apple doc:
If the prefersLargeTitles property of the navigation bar is false, this property has no effect and the navigation item’s title is always displayed as a small title.
This is an issue you have on iOS11/12 but on iOS13 it will be surfaced a bit differently.