How to set bar button item background image globally in iOS 13

iOS 13 has a whole new set of classes for configuring navigation bars and bar button items:

UIBarAppearance
UINavigationBarAppearance
UIBarButtonItemAppearance
UIBarButtonItemStateAppearance

How do I use these to give bar button items a global appearance? Let's say I want all bar button items to have a common background image. I used to say:

UIBarButtonItem.appearance().setBackgroundImage(im, for:.normal, barMetrics:.default)

This seems to be just what is superseded by these new classes. So what's the right way now?

Solution

It's verbose, but in some ways it's clearer. You can configure a navigation bar appearance and assign it to the navigation bar's standardAppearance through the proxy:

    let app = UIBarButtonItemAppearance()
    app.normal.backgroundImage = im
    let navbarapp = UINavigationBarAppearance()
    navbarapp.configureWithOpaqueBackground()
    navbarapp.buttonAppearance = app
    UINavigationBar.appearance().standardAppearance = navbarapp

The only problem with that is that it assigns the same background image to back button items. So if that's not desired, you have to code defensively, assigning back button items an empty (not nil) image:

    let app = UIBarButtonItemAppearance()
    app.normal.backgroundImage = im
    let navbarapp = UINavigationBarAppearance()
    navbarapp.configureWithOpaqueBackground()
    navbarapp.buttonAppearance = app
    let back = UIBarButtonItemAppearance()
    back.normal.backgroundImage = UIImage() // prevent back button item
    navbarapp.backButtonAppearance = back
    UINavigationBar.appearance().standardAppearance = navbarapp