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How to preview your layout at different Dynamic Type sizes

Paul Hudson    @twostraws   

Fully updated for Xcode 11.2

When building apps it’s critical to make sure your layouts work great with all ranges of Dynamic Type. This is partly because SwiftUI natively supports it, partly because many people use smaller font sizes because they want a higher information density, but mostly because many people with accessibility needs rely on it.

Fortunately, all of SwiftUI’s components natively adapt to Dynamic Type sizes, and it’s even easy to preview your designs at various sizes by using the \.sizeCategory environment value in your preview

For example, if you wanted to see how a view looks with extra small text, you would add .environment(\.sizeCategory, .extraSmall) to your content view preview, like this:

#if DEBUG
struct ContentView_Previews: PreviewProvider {
   static var previews: some View {
      Group {
         ContentView()
            .environment(\.sizeCategory, .extraSmall)
      }
   }
}
#endif

You can also send back a group of previews, all using different size categories. This allows you to see the same design at various font sizes side by side.

So, this code shows the design at extra small size, regular size, and the largest possible size:

#if DEBUG
struct ContentView_Previews: PreviewProvider {
   static var previews: some View {
      Group {
         ContentView()
            .environment(\.sizeCategory, .extraSmall)

         ContentView()

         ContentView()
            .environment(\.sizeCategory, .accessibilityExtraExtraExtraLarge)   
      }
   }
}
#endif

If your design works great across all three of those, you’re good to go.

Tip: If your preview is zoomed right in, you should either scroll around or zoom out to the other previews.

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