writing to Binding inside a Button action triggers onDisappear - ios

Question

I have a struct:
struct Demo {
struct Data {
var value: Int
}
var data: [Data]
}
and then in some view I have:
struct SomeView: View {
#Binding var demo: Demo
var body: some View {
Button(action: {
demo.data[validIndex].value = 5
}) {
Image(systemName: "plus.circle")
.resizable()
.frame(width: 50.0, height: 50.0, alignment: .center)
}
}
}
assume the var data: [Data] has more than 5 elements in it, and we're just trying to update an existing value when we press this button in SomeView. If I use SomeView like this:
struct DisappearView: View {
#Binding var demo: Demo
var body: some View {
ZStack {
// other views/shapes, etc
SomeView(demo: $demo)
}
.onAppear {
// do some stuff
}
.onDisappear {
// do some stuff
}
}
}
The data comes from:
class DemoStore: ObservableObject {
#Published var demos: [Demo] = []
// assume this loads correctly and demos is populated
}
The access to DemoStore and demos getting passed around looks like this:
import SwiftUI
#main
struct App: App {
#StateObject private var store = DemoStore()
var body: some Scene {
WindowGroup {
NavigationView {
DemosView(demos: $store.demos) { }
}
}
}
}
struct DemosView: View {
#Binding var demos: [Demo]
var body: some View {
List($demos) { $demo in
NavigationLink(destination: DisappearView(demo: $demo)) {
}
}
}
}
the write line, demo.data[validIndex].value = 5 upon button press triggers the .onDisappear in the parent View, and I cannot figure out why. I've used the debugger to step through and execute the code line by line, the array update seems to work when I write it as an expression in the debugger, but if I resume the code it boots out of the view and triggers .onDisappear. If I comment out the write line, .onDisappear isn't triggered when I press the button.