How do you use UIKit in SwiftUI and SwiftUI in UIKit?

TL;DR

UIKit inside SwiftUI: UIViewRepresentable for views, UIViewControllerRepresentable for view controllers. Use a Coordinator for delegates.
SwiftUI inside UIKit: UIHostingController for screens or parts of screens, UIHostingConfiguration for cells (iOS 16).

Most real apps mix both, so interviewers ask this often.

UIKit inside SwiftUI

struct SearchBar: UIViewRepresentable {
    @Binding var text: String

    func makeUIView(context: Context) -> UISearchBar {
        let bar = UISearchBar()
        bar.delegate = context.coordinator
        return bar
    }

    func updateUIView(_ bar: UISearchBar, context: Context) {
        if bar.text != text { bar.text = text }
    }

    func makeCoordinator() -> Coordinator { Coordinator(text: $text) }

    final class Coordinator: NSObject, UISearchBarDelegate {
        var text: Binding<String>
        init(text: Binding<String>) { self.text = text }

        func searchBar(_ searchBar: UISearchBar, textDidChange searchText: String) {
            text.wrappedValue = searchText
        }
    }
}

Method	When it runs	What to do
`makeUIView`	Once	Create and configure the view
`updateUIView`	Every time SwiftUI state changes	Push new values into the view
`makeCoordinator`	Once, before `makeUIView`	Create the delegate / target object
`dismantleUIView`	When removed	Clean up observers
`sizeThatFits` (iOS 16)	During layout	Give a custom size

Rules:

Do not create the view in updateUIView. Only update it.
Compare before you set (if bar.text != text). This avoids loops and cursor jumps.
The coordinator sends UIKit events back to SwiftUI, usually through a Binding.

A view controller

struct DocumentPicker: UIViewControllerRepresentable {
    var onPick: (URL) -> Void

    func makeUIViewController(context: Context) -> UIDocumentPickerViewController {
        let picker = UIDocumentPickerViewController(forOpeningContentTypes: [.pdf])
        picker.delegate = context.coordinator
        return picker
    }

    func updateUIViewController(_ vc: UIDocumentPickerViewController, context: Context) {}

    func makeCoordinator() -> Coordinator { Coordinator(onPick: onPick) }

    final class Coordinator: NSObject, UIDocumentPickerDelegate {
        let onPick: (URL) -> Void
        init(onPick: @escaping (URL) -> Void) { self.onPick = onPick }
        func documentPicker(_ c: UIDocumentPickerViewController, didPickDocumentsAt urls: [URL]) {
            urls.first.map(onPick)
        }
    }
}

SwiftUI inside UIKit

let settings = UIHostingController(rootView: SettingsView())
navigationController?.pushViewController(settings, animated: true)

To embed it as a child:

let host = UIHostingController(rootView: BannerView(title: "Sale"))
addChild(host)
view.addSubview(host.view)
host.view.translatesAutoresizingMaskIntoConstraints = false
NSLayoutConstraint.activate([
    host.view.leadingAnchor.constraint(equalTo: view.leadingAnchor),
    host.view.trailingAnchor.constraint(equalTo: view.trailingAnchor),
    host.view.topAnchor.constraint(equalTo: view.safeAreaLayoutGuide.topAnchor)
])
host.didMove(toParent: self)
host.sizingOptions = .intrinsicContentSize // iOS 16: size follows SwiftUI content

Do not forget addChild and didMove(toParent:). Without them, appearance callbacks and environment values break.

SwiftUI in cells

cell.contentConfiguration = UIHostingConfiguration {
    HStack {
        Image(systemName: "star")
        Text(item.title)
    }
}
.margins(.all, 12)

This is great for migrating a list screen step by step.

Passing data into a hosted view

The rootView is a value. To update it, set a new rootView, or share an @Observable model:

let model = BannerModel()
let host = UIHostingController(rootView: BannerView(model: model))
model.title = "New title" // view updates automatically

Newer helpers

iOS 18: UIGestureRecognizerRepresentable wraps UIKit gesture recognizers for SwiftUI.
iOS 18: UIKit can animate with SwiftUI Animation values (UIView.animate(_ animation:)).
iOS 26: UIKit tracks @Observable models automatically. Read a property in layoutSubviews or the new updateProperties(), and UIKit updates the view when it changes.

Common follow-up questions

Why use a Coordinator instead of the struct itself? The struct is recreated often. Delegates need a stable class instance.
How do you get the environment in updateUIView? Use context.environment.
Can I call SwiftUI dismiss from UIKit? Pass a closure in, or use the Coordinator to call back.
What breaks most often? Missing addChild, sizing of hosted views, and update loops in updateUIView.

How do you use UIKit in SwiftUI and SwiftUI in UIKit?

#TL;DR

#UIKit inside SwiftUI

#A view controller

#SwiftUI inside UIKit

#SwiftUI in cells

#Passing data into a hosted view

#Newer helpers

#Common follow-up questions