Include SwiftUI views in existing UIKit application

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

---

Using SwiftUI within 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.

---

Using UIKit within 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.

---

Compatibility

Please note that you cannot use SwiftUI on iOS versions < iOS 13, as SwiftUI is only available on iOS 13 and above. See this post for more information.

If you want to use SwiftUI in a project with a target below iOS 13, you need to tag your SwiftUI structs with @available(iOS 13.0.0, *) attribute.

If you want to embed SwiftUI into a UIKit view controller, use a Container View.

class ViewController: UIViewController {
    @IBOutlet weak var theContainer: UIView!

    override func viewDidLoad() {
        super.viewDidLoad()

        let childView = UIHostingController(rootView: SwiftUIView())
        addChild(childView)
        childView.view.frame = theContainer.bounds
        theContainer.addSubview(childView.view)
        childView.didMove(toParent: self)
    }
}

Reference

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.