Binding an element of an array of an ObservableObject : 'subscript(_:)' is deprecated

Question

I\'m using an ObservableObject \'DataStore\', which contains an array (\'exampleList\') of objects (\'exampleObject\').

@Published exampleList = [exampleObjec         


        

Answer 1

I had to bind the array of an observable object recently, didn't get any warnings on stable XCode11. I did it like this

struct ScheduleTimer: Identifiable {
    var id: Int
    var name: String
    var start: Date
    var end: Date
    var isActive: Bool
}

struct ScheduleView: View {
    @ObservedObject var scheduleController = ScheduleController()
    var body: some View {
        NavigationView {
            Form {
                ForEach(scheduleController.timers) { timer in
                    ScheduleForm(scheduleController: self.scheduleController, timer: timer)
                }
            }
        }
    }
}


struct ScheduleForm: View {
    @ObservedObject var scheduleController: ScheduleController
    var timer: ScheduleTimer
    var scheduleIndex: Int {
        scheduleController.timers.firstIndex(where: { $0.id == timer.id })!
    }
    @State var start = Date()
    var body: some View {
        Section(header: Text(self.scheduleController.timers[scheduleIndex].name)){
            DatePicker("From", selection: self.$scheduleController.timers[scheduleIndex].start, displayedComponents: .hourAndMinute)
            DatePicker("To", selection: self.$scheduleController.timers[scheduleIndex].end, displayedComponents: .hourAndMinute)
            Toggle(isOn: self.$scheduleController.timers[scheduleIndex].isActive) {
                Text("")
            }.toggleStyle(DefaultToggleStyle())
        }
    }
}

class ScheduleController: ObservableObject {
    @Published var timers = [ScheduleTimer]()
...

Answer 2

Xcode 11, beta 6 UPDATE:

Good news! Just as I suspected, in beta 6, the Binding conformance to MutableCollection has been been replaced with something else. Instead of conforming to MutableCollection, it now let your access the elements via @dynamicMemberLookup. The result is you now can keep doing $text[3] and no longer get a warning! It seems this question can be closed now.

Xcode 11, beta 5. Old answer:

I finally got some time to investigate this a little. As I mentioned in the comments, I think it would be wise to wait until the Collection conformance is completely removed (or replaced with something else). But just to satisfy our curiosity, I have created an extension on Binding, that I think does what the current Collection conformance does. The only difference is that, instead of accessing through a subscript, I implemented a function called element(_ idx: Int) to get a Binding<T> to the element.

If one day the conformance is completely removed, I may change the implementation, and conform to Collection myself. I cannot do it now, because it would conflict with the existent (and deprecated) implementation. For the time being, I think this demonstrate how to handle the warnings if you absolutely want to get rid of them.

Just to be clear. I am not using this code. As long as I can still access the elements through the subscript, I will still do it and ignore the warnings. This is just for academic purposes.

The extension is:

extension Binding where Value: MutableCollection, Value.Index == Int {
    func element(_ idx: Int) -> Binding<Value.Element> {
        return Binding<Value.Element>(
            get: {
                return self.wrappedValue[idx]
        }, set: { (value: Value.Element) -> () in
            self.wrappedValue[idx] = value
        })
    }
}

And it can be used like this:

struct MainView: View {
    @Binding var text: [String]

    var body: some View {
        TextField("", text: $text.element(0))
        TextField("", text: $text.element(1))
        TextField("", text: $text.element(2))
    }
}