07 May 2023

SwiftUI binding in UIKit with UIHostingController and ObservableObject

Often I have found myself wanting to use SwiftUI data bindings in Views hosted via UIHostingController in UIKit. A great example of this is when you want to use a SwiftUI View in a MKAnnotationView which has a data binding in the SwiftUI View.

Obviously, UIKit and SwiftUI don’t work with the @State of @Binding property wrappers, however @ObservedObject still works well and changes made on the UIKit code are propagated down to the SwiftUI View. Magic!

This allows us to create a View Model for our SwiftUI View, declare it on the UIKit class and bind the changes in the UIKit code to the SwiftUI View.

The SwiftUI code:

struct MapMarkerView: View {
    class ViewModel : ObservableObject {
        @Published var color: Color = .red
    @ObservedObject var viewModel: ViewModel
    var body: some View {

The UIKit code:

class MapMarkerAnnotationView : MKAnnotationView {
    var viewModel = MapMarkerView.ViewModel()
    override init(annotation: MKAnnotation?, reuseIdentifier: String?) {
        super.init(annotation: annotation, reuseIdentifier: reuseIdentifier)
        let vc = UIHostingController(rootView: MapMarkerView(viewModel: self.viewModel))
        guard let view = vc.view {
            view.frame = bounds
    @available(*, unavailable)
    required init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    func setColor(color: UIColor) {
        self.viewModel.color = Color(color)

Now when you call setColor the color in the MapMarkerView will be updated through the ObservedObject binding. Pretty neat!

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