Pass #Published properties from view controllers to SwiftUI - ios

Question

Suppose you have a legacy view controller that I'd like to use with SwiftUI. The view controller has one #Published property that contains it current state:
class LegacyViewController: UIViewController {
enum State {
case opened
case closed
case halfOpened
}
#Published var state: State
override init(nibName nibNameOrNil: String?, bundle nibBundleOrNil: Bundle?) {
self.state = .closed
super.init(nibName: nil, bundle: nil)
}
override func viewDidLoad() {
super.viewDidLoad()
// state is changed after some time
}
}
Ideally, I'd like to use it with SwiftUI like this:
struct ContentView: View {
#State var state: LegacyViewController.State
var body: some View {
VCWrapper(state: $state).overlay (
Text("\(state)")
)
}
}
which would mean that I need to implement UIViewControllerRepresentable protocol:
struct VCWrapper: UIViewControllerRepresentable {
#Binding var state: LegacyViewController.State
func makeUIViewController(context: Context) -> LegacyViewController {
let vc = LegacyViewController(nibName: nil, bundle: nil)
/// where to perform the actual binding?
return vc
}
func updateUIViewController(_ uiViewController: LegacyViewController, context: Context) {
}
}
However, I'm having trouble figuring out where to do the actual binding from state property of the LegacyViewController to the state property exposed by VCWrapper. If LegacyViewController exposed a delegate, I could implement the binding through the Coordinator object, but I'm not so sure how to do this considering that I don't use a delegate object?

Answer 1

Here is possible solution - use Combine. Tested with Xcode 12 / iOS 14.
import Combine
struct VCWrapper: UIViewControllerRepresentable {
#Binding var state: LegacyViewController.State
func makeUIViewController(context: Context) -> LegacyViewController {
let vc = LegacyViewController(nibName: nil, bundle: nil)
// subscribe to controller state publisher and update bound
// external state
context.coordinator.cancelable = vc.$state
.sink {
DispatchQueue.main.async {
_state.wrappedValue = $0
}
}
return vc
}
func updateUIViewController(_ uiViewController: LegacyViewController, context: Context) {
}
func makeCoordinator() -> Coordinator {
Coordinator()
}
class Coordinator {
var cancelable: AnyCancellable?
}
}