Not_updating_based_on_ObservedObject.md

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Q: SwiftUI View not updating based on @ObservedObject (by Anton)

@ObservedObject var numberLine = NumberLine()

var body: some View {
    VStack {
        HStack {
            ForEach(0 ..< numberLine.visible.count) { number in
                if self.numberLine.visible[number] {
                    Text(String(number)).font(.title).padding(5)
                }
            }

A: With @ObservedObject everything's fine... let's analyse...

Iteration 1:

Take your code without changes and add just the following line (shows as text current state of visible array)

VStack { // << right below this
    Text("\(numberLine.visible.reduce(into: "") { $0 += $1 ? "Y" : "N"} )")

and run, and you see that Text is updated so observable object works

Iteration 2:

Remove self.numberLine.objectWillChange.send() and use instead default @Published pattern in view model

class NumberLinex: ObservableObject {
    @Published var visible: [Bool] = Array(repeatElement(true, count: 10))
}

run and you see that update works the same as on 1st demo above.

*But... main numbers in ForEach still not updated... yes, because problem in ForEach - you used constructor with Range that generates constant view's group by-design (that documented!).

!! That is the reason - you need dynamic ForEach, but for that model needs to be changed.

Iteration 3 - Final:

Dynamic ForEach constructor requires that iterating data elements be identifiable, so we need struct as model and updated view model.

Here is final solution & demo (tested with Xcode 11.4 / iOS 13.4)

struct ContentView: View {

    @ObservedObject var numberLine = NumberLine()

    var body: some View {
        VStack {
            HStack {
                ForEach(numberLine.visible, id: \.id) { number in
                    Group {
                        if number.visible {
                            Text(String(number.id)).font(.title).padding(5)
                        }
                    }
                }
            }.padding()

            Button("Change") {
                let index = Int.random(in: 0 ..< self.numberLine.visible.count)
                self.numberLine.visible[index].visible.toggle()
            }.padding()
        }
    }
}

class NumberLine: ObservableObject {
    @Published var visible: [NumberItem] = (0..<10).map { NumberItem(id: $0) }
}

struct NumberItem {
    let id: Int
    var visible = true
}