Passing Value from SwiftUI to UIViewController Using UIHostingController - ios

Question

I have a SwiftUI view, which consists of a TextField. I want that whenever I type in the TextField it should send the value to the control on the UIKit UIViewController.
// Here is the ContentView
class ContentViewDelegate: ObservableObject {
var didChange = PassthroughSubject<ContentViewDelegate, Never>()
var name: String = "" {
didSet {
self.didChange.send(self)
}
}
}
struct ContentView: View {
#ObservedObject var delegate: ContentViewDelegate
init(delegate: ContentViewDelegate) {
self.delegate = delegate
}
var body: some View {
VStack {
TextField("Enter name", text: self.$delegate.name)
.textFieldStyle(RoundedBorderTextFieldStyle())
}.padding()
.background(Color.green)
}
}
I checked didChange does get fired in the above code. But in the code below, the sink is never fired.
class ViewController: UIViewController {
private var delegate = ContentViewDelegate()
private var contentView: ContentView!
override func viewDidLoad() {
super.viewDidLoad()
self.contentView = ContentView(delegate: self.delegate)
let controller = UIHostingController(rootView: self.contentView)
controller.view.translatesAutoresizingMaskIntoConstraints = false
self.addChild(controller)
self.view.addSubview(controller.view)
controller.didMove(toParent: self)
NSLayoutConstraint.activate([
controller.view.widthAnchor.constraint(equalToConstant: 200),
controller.view.heightAnchor.constraint(equalToConstant: 44),
controller.view.centerXAnchor.constraint(equalTo: self.view.centerXAnchor),
controller.view.centerYAnchor.constraint(equalTo: self.view.centerYAnchor)
])
_ = self.delegate.didChange.sink { delegate in
print(delegate.name)
}
}
Any ideas why didChange.sink is not getting fired?

Answer 1

If you assign the publisher to _ then it is deallocated when viewDidLoad returns. Early examples from Apple show the assignment to _ and it used to work.
You need to ensure you keep a strong reference to your publisher using a property:
class ViewController: UIViewController {
private var delegate = ContentViewDelegate()
private var contentView: ContentView!
private var textChangePublisher: AnyCancellable?
override func viewDidLoad() {
super.viewDidLoad()
self.contentView = ContentView(delegate: self.delegate)
let controller = UIHostingController(rootView: self.contentView)
controller.view.translatesAutoresizingMaskIntoConstraints = false
self.addChild(controller)
self.view.addSubview(controller.view)
controller.didMove(toParent: self)
NSLayoutConstraint.activate([
controller.view.widthAnchor.constraint(equalToConstant: 200),
controller.view.heightAnchor.constraint(equalToConstant: 44),
controller.view.centerXAnchor.constraint(equalTo: self.view.centerXAnchor),
controller.view.centerYAnchor.constraint(equalTo: self.view.centerYAnchor)
])
self.textChangePublisher = self.delegate.didChange.sink { delegate in
print(delegate.name)
}
}