Set property on ViewController in UIViewControllerRepresentable - swift

Question

How can I change a property on a UIViewController presented via. a UIViewControllerRepresentable ?
Sample code of how I would expect it to work, however it doesn't. How can I make it work?
(color is just a example, please don't focus on that)
class MyViewController: UIViewController {
var color: UIColor? = nil {
didSet {
guard isViewLoaded else { return }
view.layer.backgroundColor = color?.cgColor
}
}
override func viewDidLoad() {
view.layer.backgroundColor = color?.cgColor
}
}
struct MyView: UIViewControllerRepresentable {
#State private var color: UIColor?
func makeUIViewController(context: UIViewControllerRepresentableContext<MyView>) -> MyViewController {
let viewController = MyViewController()
viewController.color = color // always nil?
return viewController
}
func updateUIViewController(_ uiViewController: MyViewController,
context: UIViewControllerRepresentableContext<MyView>) {
uiViewController.color = color // always nil?
}
}
extension MyView {
func color(_ color: UIColor) -> MyView {
self.color = color // does nothing?
return self
}
}
struct ContentView: View {
var body: some View {
MyView()
.color(.magenta)
}
}

Answer 1

Here is possible approach (if you expect that color can be modified externally, as it is seen). Tested with Xcode 11.4 / iOS 13.4
struct MyView: UIViewControllerRepresentable {
#Binding var color: UIColor?
func makeUIViewController(context: UIViewControllerRepresentableContext<MyView>) -> MyViewController {
let viewController = MyViewController()
viewController.color = color // always nil?
return viewController
}
func updateUIViewController(_ uiViewController: MyViewController,
context: UIViewControllerRepresentableContext<MyView>) {
uiViewController.color = color // always nil?
}
}
struct ContentView: View {
#State private var color: UIColor? = .magenta
var body: some View {
MyView(color: $color)
// MyView(color: .constant(.magenta)) // alternate usage
}
}

Answer 2

Another solution based on idea from Asperi's answer:
struct MyView: UIViewControllerRepresentable {
private class State: ObservableObject {
var color: UIColor?
}
#Binding private var state: State
init() {
_state = .constant(State())
}
func makeUIViewController(context: UIViewControllerRepresentableContext<MyView>) -> MyViewController {
return MyViewController()
}
func updateUIViewController(_ uiViewController: MyViewController,
context: UIViewControllerRepresentableContext<MyView>) {
uiViewController.color = state.color
}
}
extension MyView {
func color(_ color: UIColor) -> MyView {
self.state.color = color
return self
}
}
Or a even simpler version, we just use #Binding for the wrapped ViewController directly
struct MyView: UIViewControllerRepresentable {
#Binding private var viewController: MyViewController
init() {
_viewController = .constant(MyViewController())
}
func makeUIViewController(context: UIViewControllerRepresentableContext<MyView>) -> MyViewController {
return viewController
}
func updateUIViewController(_ uiViewController: MyViewController,
context: UIViewControllerRepresentableContext<MyView>) {
}
}
extension MyView {
func color(_ color: UIColor) -> MyView {
self.viewController.color = color
return self
}
}