How can I change the default font for UIBarButtonItems?

Question

I want to change the default font for all UIBarButtonItems. I have the following code in the root view controller of my app:

    let attributes: [NSAttributedString.Key: Any] = [.font: UIFont.systemFont(ofSize: 30)]
    UIBarButtonItem.appearance().setTitleTextAttributes(attributes, for: .normal)
    UINavigationBar.appearance().titleTextAttributes = attributes
    UINavigationBarAppearance().buttonAppearance.normal.titleTextAttributes = attributes
    UIBarButtonItemAppearance().normal.titleTextAttributes = attributes
    self.navigationItem.rightBarButtonItem = UIBarButtonItem(title: "foo", style: .plain, target: nil, action: nil)

That bar button item's font is still the default, despite the appearance changes. How can I set a default font? I know I can set the font for each individual bar button item, but I'm looking for a way to change it broadly.

Answer 1

iOS 13 before

class AppDelegate : NSObject, UIApplicationDelegate {

    func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey : Any]? = nil) -> Bool {

        if #available(iOS 13, *) {

        }else{
            let attributes: [NSAttributedString.Key: Any] = [.font: UIFont.systemFont(ofSize: 30)]
            UIBarButtonItem.appearance().setTitleTextAttributes(attributes, for: .normal)
            UINavigationBar.appearance().titleTextAttributes = attributes
        }

        return true
    }
}

iOS 13

class MyNavigationController : UINavigationController {

    override init(rootViewController: UIViewController) {
        super.init(rootViewController: rootViewController)
        if #available(iOS 13, *) {
            let attributes: [NSAttributedString.Key: Any] = [.font: UIFont.systemFont(ofSize: 30)]
            let appearance = UINavigationBarAppearance()
            appearance.buttonAppearance.normal.titleTextAttributes = attributes
            appearance.titleTextAttributes = attributes
            self.navigationBar.standardAppearance = appearance
        }
    }

    required init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
}

Answer 2

You can use UINavigationBarAppearance to customize all navigation bars, but you need to set the standardAppearance on the navigation bar's appearance proxy – calls like these:

UINavigationBarAppearance().buttonAppearance.normal.titleTextAttributes = attributes
UIBarButtonItemAppearance().normal.titleTextAttributes = attributes

in isolation do nothing, as they create a new appearance, set a value, then throw it away. Instead do this:

let appearance = UINavigationBarAppearance()
appearance.buttonAppearance.normal.titleTextAttributes = attributes
UINavigationBar.appearance().standardAppearance = appearance