Note

The #Preview macro (WWDC23 session) will supplant this library once you can set your Minimum Deployment to iOS 17 or higher.

If you have a project on Xcode 14, or your Minimum Deployment target is set to as early as iOS 11, then this still may be the library you're looking for.

PreviewView

Make use of SwiftUI previews for rapidly prototyping your UIViewControllers and UIViews!

The SwiftUI preview canvas is tied to a specific version of Xcode, not the the target OS version. This means you can make use of this utility even if you're not targeting iOS 13 or higher, as long as you're using Xcode 10 or higher.

My iOS deployment target is below iOS 13

If you're targeting an iOS version earlier than iOS 13 then you may be get an error such as:

Compiling failed: '__designTimeString(_:fallback:)' is only available in iOS 13.0 or newer

Other known variants may be:

• __designTimeInteger(_:fallback:)
• __designTimeBoolean(_:fallback:)
• __designTimeFloat(_:fallback:)

To solve this issue this library provides another target, PreviewViewLegacyOSCompileFix, which adds functions annotated with @backDeployed(before:) so these functions exist on versions earlier than iOS 13.

In addition the normal import PreviewView and import SwiftUI imports alongside your PreviewProvider you will need to add import PreviewViewLegacyOSCompileFix to ensure the back deployed functions are present.

Don't forget to mark your PreviewProvider with @available(iOS 13, *).

Installation

You can manually drop the files into your project, or take a look at Apple's documentation for adding Swift Packages in Xcode.

Adding this as a dependency on a Swift Package is not recommended as it will then force the dependency on anyone that consumes your library.

Previewing a view

struct YourViewController_Previews: PreviewProvider {
    static var previews: some View {
        ViewPreview(YourView())
            .previewLayout(.fixed(width: 375, height: 86))
    }
}

Important: Update the previewLayout values to be the typical size of your view.

Previewing a view controller

Standalone

struct YourViewController_Previews: PreviewProvider {
    static var previews: some View {
        ViewControllerPreview(YourViewController())
            .edgesIgnoringSafeArea(.all)
    }
}

If you wish to test a custom UINavigationController you can do so with ViewControllerPreview.

struct YourNavigationController_Previews: PreviewProvider {
    static var previews: some View {
        ViewControllerPreview(YourNavigationController())
            .edgesIgnoringSafeArea(.all)
    }
}

Embedded in a UINavigationController

struct YourViewController_Previews: PreviewProvider {
    static var previews: some View {
        NavigationControllerPreview {
            YourViewController()
        }
        .edgesIgnoringSafeArea(.all)
    }
}

The body content of the NavigationControllerPreview accepts an entire navigation stack, allowing your previews to show back bar button items, and even be navigatable in Live Preview.

struct DetailViewController_Previews: PreviewProvider {
    static var previews: some View {
        NavigationControllerPreview {
            ListViewController()
            DetailViewController()
        }
        .edgesIgnoringSafeArea(.all)
    }
}

You can customise the navigation bar settings and toolbar settings of the navigation controller via the initializer parameters.

struct DetailViewController_Previews: PreviewProvider {
    static var previews: some View {
        NavigationControllerPreview(barStyle: .largeTitle, showsToolbar: true) {
            ListViewController()
            DetailViewController()
        }
        .edgesIgnoringSafeArea(.all)
    }
}

Embedded in a UITabBarController

struct YourViewController_Previews: PreviewProvider {
    static var previews: some View {
        TabBarControllerPreview {
            ViewControllerPreview(YourViewController())
        }
        .edgesIgnoringSafeArea(.all)
    }
}

Displaying a single tab would be weird, so to allow your previews to closely match your real app you can provide the other tabs within the body.

struct YourViewController_Previews: PreviewProvider {
    static var previews: some View {
        TabBarControllerPreview {
            PreviewBlankTabItem(title: "First", image: UIImage(systemName: "capsule"))
            
            ViewControllerPreview(YourViewController())
            
            ViewControllerPreview(YourOtherViewController())
        }
        .edgesIgnoringSafeArea(.all)
    }
}

You can even embed your view controllers in a navigation controller to get the full in-app experience.

struct YourViewController_Previews: PreviewProvider {
    static var previews: some View {
        TabBarControllerPreview {
            PreviewBlankTabItem(title: "First", image: UIImage(systemName: "capsule"))
            
            NavigationControllerPreview {
                YourViewController()
            }
            
            PreviewBlankTabItem(title: "Third", image: UIImage(systemName: "diamond"))
        }
        .edgesIgnoringSafeArea(.all)
    }
}