Why don't changes to #ObservedObject update a UIViewRepresentable? - ios

Question

I have this simple example where I'm creating an #ObservedObject in a parent view and passing it to a child UIViewRepresentable. When I click "Button", it modifies the #ObservableObject but the child view never gets updated (i.e updateUIView is never called). Is there a different way to do this?
import SwiftUI
class UpdateViewState: ObservableObject {
#Published var words = ["A", "B", "C"]
func addWord(word: String) {
print("added word")
words.append(word)
}
}
struct UpdateView: View {
#ObservedObject private var state = UpdateViewState()
var body: some View {
VStack {
UpdateViewRepresentable(state: state)
Text("Button").onTapGesture {
self.state.addWord(word: "A")
}
}
}
}
struct UpdateViewRepresentable: UIViewRepresentable {
#ObservedObject var state: UpdateViewState
func makeUIView(context: Context) -> UILabel {
let view = UILabel()
view.text = "Hello World"
return view
}
func updateUIView(_ uiView: UILabel, context: UIViewRepresentableContext<UpdateViewRepresentable>) {
print("updateUIView")
uiView.text = state.words.joined(separator: ", ")
}
}

Answer 1

try this:
public final class UpdateViewState: ObservableObject {
#Published var words = ["A", "B", "C"]
func addWord(word: String) {
print("added word ", words)
words.append(word)
}
}
struct ContentView: View {
#EnvironmentObject private var state: UpdateViewState
var body: some View {
VStack {
UpdateViewRepresentable(state: .constant(state))
Text("Button").onTapGesture {
self.state.addWord(word: "A")
}
}.onAppear() {
self.state.words.append("aha")
}
}
}
struct UpdateViewRepresentable: UIViewRepresentable {
#Binding var state: UpdateViewState
func makeUIView(context: Context) -> UILabel {
let view = UILabel()
view.text = "Hello World"
return view
}
func updateUIView(_ uiView: UILabel, context: UIViewRepresentableContext<UpdateViewRepresentable>) {
print("updateUIView")
uiView.text = state.words.joined(separator: ", ")
}
}

Answer 2

This may help you in a very simple way:
var body: some View {
VStack {
UpdateViewRepresentable(state: state)
Text("Button").onTapGesture {
self.state.addWord(word: "A")
self.state.objectWillChange.send()
}
}
}
Try to use the line I added, this will the View to update itself. Make sure you use:
import Combine