Include SwiftUI views in existing UIKit applicatio

Question

Is is possible to build views with SwiftUI side by side with an existing UIKit application?

I have an existing application written in Objective-C. I've begun migrating to Swift 5. I'm wondering if I can use SwiftUI alongside my existing UIKit .xib views.

That is to say I want some views built with SwiftUI and some other views built with UIKit in the same app. Not mixing the two of course.

SomeObjCSwiftProject/
    SwiftUIViewController.swift
    SwiftUIView.xib
    UIKitViewController.swift
    UIKitView.xib

Working alongside each other

Answer 1

Others has been showcasing how to use UIHostingController.

I can show how you can present a UIViewController from SwiftUI UIViewControllerRepresentable:

struct YourViewControllerWrapper: UIViewControllerRepresentable {
    typealias UIViewControllerType = YourViewController

    func makeUIViewController(context: UIViewControllerRepresentableContext<YourViewControllerWrapper>) -> YourViewController {
        let storyBoard = UIStoryboard(name: "YourStoryboard", bundle: Bundle.main)
        return storyBoard.instantiateViewController(withIdentifier: "YourViewController") as! YourViewController
    }

    func updateUIViewController(_ uiViewController: YourViewController, context: UIViewControllerRepresentableContext<YourViewController>) {
        // do nothing
    }
}

Answer 2

import Foundation
    #if canImport(SwiftUI)
    import SwiftUI

internal final class SomeRouter {
    fileprivate weak var presentingViewController: UIViewController!

    function navigateToSwiftUIView() {
       if #available(iOS 13, *) {
            let hostingController = UIHostingController(rootView: contentView())  
presentingViewController?.navigationController?.pushViewController(hostingController, animated: true)
            return
        }
        //Keep the old way when not 13.
}
#endif

Answer 3

If you're looking to create a SwiftIU view from a legacy Objective C project, then this technique worked perfectly for me,

See Adding SwiftUI to Objective-C Apps

Kudos to our friend who wrote that up.

Answer 4

One item I have not seen mentioned yet, and involves Xcode 11 beta 5 (11M382q) involves updating your app's info.plist file.

For my scenario, I am taking an existing Swift & UIKit based application and fully migrating it to be an iOS 13 & pure SwiftUI app, so backwards compatibility is not a concern for me.

After making the necessary changes to AppDelegate:

// MARK: UISceneSession Lifecycle
func application(_ application: UIApplication,
                 configurationForConnecting connectingSceneSession: UISceneSession,
                 options: UIScene.ConnectionOptions) -> UISceneConfiguration {
    return UISceneConfiguration(name: "Default Configuration",
                                sessionRole: connectingSceneSession.role)
}

And adding in a SceneDelegate class:

import UIKit
import SwiftUI

class SceneDelegate: UIResponder, UIWindowSceneDelegate {

    var window: UIWindow?

    func scene(_ scene: UIScene, willConnectTo session: UISceneSession, options connectionOptions: UIScene.ConnectionOptions) {
        if let windowScene = scene as? UIWindowScene {
            let window = UIWindow(windowScene: windowScene)
            window.rootViewController = UIHostingController(rootView: HomeList())
            self.window = window
            window.makeKeyAndVisible()
        }
    }
}

I was encountering a problem where my SceneDelegate was not being called. This was fixed by adding the following into my info.plist file:

<key>UIApplicationSceneManifest</key>
<dict>
    <key>UIApplicationSupportsMultipleScenes</key>
    <false/>
    <key>UISceneConfigurations</key>
    <dict>
        <key>UIWindowSceneSessionRoleApplication</key>
        <array>
            <dict>
                <key>UISceneClassName</key>
                <string></string>
                <key>UISceneDelegateClassName</key>
                <string>$(PRODUCT_MODULE_NAME).SceneDelegate</string>
                <key>UISceneConfigurationName</key>
                <string>Default Configuration</string>
                <key>UISceneStoryboardFile</key>
                <string>LaunchScreen</string>
            </dict>
        </array>
    </dict>
</dict>

And a screenshot to see:

The main items to keep in sync are:

• Delegate Class Name so that Xcode knows where to find your SceneDelegate file
• Configuration Name so that the call in AppDelegate can load the correct UISceneConfiguration

After doing this, I was then able to load my newly created HomeList view (A SwiftUI object)

Answer 5

UIHostingController

Although at the moment the documentation for the class has not been written, UIHostingController<Content> seems to be what you're looking for: https://developer.apple.com/documentation/swiftui/uihostingcontroller

I've just tried it in my app with the following line of code:

let vc = UIHostingController(rootView: BenefitsSwiftUIView())

Where BenefitsSwiftUIView is just the default "Hello World" View from SwiftUI. This works exactly as you expect it. It also works if you subclass UIHostingController.

Answer 6

edit 05/06/19: Added information about UIHostingController as suggested by @Departamento B in his answer. Credits go to him!

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Using SwiftUI with UIKit

One can use SwiftUI components in existing UIKit environments by wrapping a SwiftUI View into a UIHostingController like this:

let swiftUIView = SomeSwiftUIView() // swiftUIView is View
let viewCtrl = UIHostingController(rootView: swiftUIView)

It's also possible to override UIHostingController and customize it to one's needs, e. g. by setting the preferredStatusBarStyle manually if it doesn't work via SwiftUI as expected.

UIHostingController is documented here.

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Using UIKit with SwiftUI

If an existing UIKit view should be used in a SwiftUI environment, the UIViewRepresentable protocol is there to help! It is documented here and can be seen in action in this official Apple tutorial.

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Compatibility

Please note that UIKit and SwiftUI components can only be used in conjunction if the app targets iOS 13+, as SwiftUI is only available iOS 13+. See this post for more information.