How to resize Title in a navigation bar dynamically

Question

I have some views that show up in a navigation controller. Two of these views have a longer title for the navigation bar.

The problem is that when the title is too

Answer 1

Swift 5 and iOS 13 / iOS 14

The answers from above don't work if you have a large title in Swift 5 and iOS 13 because they simply add another title to your navigation bar. Instead you could use the largeTitleTextAttributes property (available since iOS 11) to shrink your title when needed.
Assuming you have set your large title via storyboard or code already, you can use the following method:

private func configureNavigationTitle(_ title: String) {
        let tempLabel = UILabel()
        tempLabel.font = UIFont.systemFont(ofSize: 34, weight: .bold)
        tempLabel.text = title

        if tempLabel.intrinsicContentSize.width > UIScreen.main.bounds.width - 30 {
            var currentTextSize: CGFloat = 34
            for _ in 1 ... 34 {
                currentTextSize -= 1
                tempLabel.font = UIFont.systemFont(ofSize: currentTextSize, weight: .bold)
                if tempLabel.intrinsicContentSize.width < UIScreen.main.bounds.width - 30 {
                    break
                }
            }
            navigationController?.navigationBar.largeTitleTextAttributes = [NSAttributedString.Key.font : UIFont.systemFont(ofSize: currentTextSize, weight: .bold)]
        }
        self.title = title
    }

So essentially we are ussing a helper label in order to get the width of our title and then we are going to shrink the font size until the title fits in our navigation bar. Call it from viewDidLoad():

override func viewDidLoad() {
        super.viewDidLoad(
        configureNavigationTitle("A very long title which fits perfectly fine")
    }