How do I change navigationBar font in Swift?

Try this:

self.navigationController.navigationBar.titleTextAttributes = [ NSFontAttributeName: UIFont(name: "CaviarDreams", size: 20)!]

Edit: Now, UIFont must be unwrapped to be able to be used here.

Swift 5 (+ safe handling of optional UIFont)

self.navigationController?.navigationBar.titleTextAttributes = [ NSAttributedString.Key.font: UIFont(name: "Caviar-Dreams", size: 20) ?? UIFont.systemFont(ofSize: 20)]