swift - Include SwiftUI views in existing UIKit application

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

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 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.

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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.

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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.