Change the navigation bar font

I wanted to set a SwiftUI iOS app in SF Rounded. It’s a system font, so I thought it’d be pretty easy. On the web, it would take like two lines of CSS.

Setting the font of the content to SF Rounded was pretty easy — just call the fontDesign(.rounded) on the root view:

@main
struct myApp: App {
  var body: some Scene {
    WindowGroup {
      ContentView()
        .fontDesign(.rounded)
    }
  }
}

Setting the font of the navigation bar, though, turned out to be surprisingly hard! I don’t think you can actually do it in SwiftUI alone — you need to pull out some UIKit APIs.

I asked on Bluesky and got some very nice help from Mark Malstrom. A lot of resources online seem to recommend similar approaches: creating an instance of UINavigationBarAppearance and setting UINavigationBar.appearance().standardAppearance to that instance:

@main
struct myApp: App {
  init() {
    guard let descriptor = UIFontDescriptor
      .preferredFontDescriptor(withTextStyle: .headline)
      .withDesign(.rounded) else {
        return
      }

    let appearance = UINavigationBarAppearance()
    appearance.titleTextAttributes = [
      .font: UIFont(descriptor: descriptor, size: 0)
    ]

    UINavigationBar.appearance().standardAppearance = appearance
  }

  var body: some View {
    // ...
  }
}

(Some resources will also tell you to set the compactAppearance and scrollEdgeAppearance properties, but Apple’s documentation says that if those are set to nil it applies the standardAppearance in those cases.)

On the other hand, some resources recommended mutating UINavigationBar.appearance() directly:

@main
struct myApp: App {
  init() {
    guard let descriptor = UIFontDescriptor
      .preferredFontDescriptor(withTextStyle: .headline)
      .withDesign(.rounded) else {
        return
      }

    UINavigationBar.appearance().titleTextAttributes = [
      .font: UIFont(descriptor: descriptor, size: 0)
    ]
  }

  var body: some View {
    // ...
  }
}

The first seems better documented, and Claude tells me that the second is a deprecated way of accomplishing it, so I went with that one.