How to update a struct in a Class from another View? (Swift) - swiftui

Question

Currently I am trying to update the count in a SingleDay struct inside a Days class from from the TestScreen view.The SingleDay struct is also in an array in Days. The change in count should be reflected in the UpdatingArrayElements view. So far I am running into this error:
Left side of mutating operator isn't mutable: 'day' is a 'let' constant"
and I have absolutely no idea on how to resolve this issue. I would appreciate any help given that I am still a beginner in iOS development and still trying to get the hang of building more complex iOS apps, thanks!
import SwiftUI
struct SingleDay: Identifiable {
let id: String = UUID().uuidString
let day: Int
var count: Int
}
class Days: ObservableObject {
#Published var daysArray: [SingleDay] = []
init() {
daysArray.append(SingleDay(day: 1, count: 0))
}
}
struct UpdatingArrayElements: View {
#StateObject var days: Days = Days()
var body: some View {
NavigationView {
List {
ForEach(days.daysArray) { day in
HStack{
Text("Day: \(day.day)")
Text("Count: \(day.count)")
}
}
}
.navigationBarItems(trailing:
NavigationLink(destination: TestScreen(dayViewModel: days), label: {
Image(systemName: "arrow.right")
.font(.title)
})
)
}
}
}
struct TestScreen: View {
#Environment(\.presentationMode) var presentationMode
#ObservedObject var dayViewModel: Days
var body: some View {
ZStack {
Color.green.ignoresSafeArea()
VStack {
ForEach(dayViewModel.daysArray) { day in
Text(String(day.day))
Button(action: {
day.count += 1
}, label: {
Text("Add count")
})
}
}
}
}
}
struct UpdatingArrayElements_Previews: PreviewProvider {
static var previews: some View {
UpdatingArrayElements()
}
}

Answer 1

here you go. now we are not using the identifiable so if you want you can also remove it.
so the real problem was that the day which is of type SingleDay is a struct not a class. so foreach give us let not vars , so in case of class object we can easily update properties because they are reference type, but in case of struct we can not do that, so it means day is another copy. so even if we can update the day of struct it will still not update the daysArray element.
struct TestScreen: View {
#Environment(\.presentationMode) var presentationMode
#ObservedObject var dayViewModel: Days
var body: some View {
ZStack {
Color.green.ignoresSafeArea()
VStack {
ForEach(dayViewModel.daysArray.indices ,id : \.self) { index in
let day = dayViewModel.daysArray[index]
Text("\(day.count)")
Button(action: {
dayViewModel.daysArray[index].count = day.count + 1
print( day.count)
}, label: {
Text("Add count")
})
}
}
}
}
}