If you instantiate a class that implements ObservableObject and mark it as @StateObject in your parent view (eg. ContentView) and then pass it in to a child view through the initializer where it is marked with @ObservedObject, you can then read its properties in the child view. However, what if you want to update the object in the child view?

If I take my object in the child view and try to update it like this:

myObject.myArray[0] = anArrayElement

Xcode won't complain, but it also doesn't work. Neither does this:

myObject.myArray.remove(at: 0)

Oddly append works:

myObject.myArray.append(newElement)

So how do we share an object across views with full read/write access everywhere?

Does your class have any method to "save" the changes that you are trying to pass to the @Published var ?

@Bnerd what would that look like? It's a class, so a reference type. The object is shared across views via the @StateObject/@ObervedObject wrappers.

If I have:

myObject.myIntProperty = 1

That's all there is to do. The assignment is the "save". What extra step are you alluding to?

@Legion , is this what you are trying to achieve, change @Published from using @ObservedValue ?

class Player: ObservableObject {
    @Published var name = "Taylor"
    @Published var age = 26
}

struct PlayerNameView: View {
    @ObservedObject var player: Player
    var body: some View {
        Text("Hello, \(player.name)")
            .onTapGesture {
                changePlayer()
            }
    }

    func changePlayer() {
        var newName = player.name = "Gomez"
        print("\(newName)")
    }
}

struct ContentView: View {
    @StateObject var player = Player()
    var body: some View {

        NavigationView {
            NavigationLink(destination: PlayerNameView(player: player)) {
                       Text("Show detail view")
                   }
               }
    }

}

This is for the Day 47 challenge. I'm trying to update the timesCompleted property of one of the elements in the array of activities/habits.

For some reason I can append new elements in the child view, but I can't remove elements or replace them. Xcode provides no error messages.

@Legion , you have to post the code and tell where the issue is, i will give it a try

Activity Struct:

struct Activity : Codable, Identifiable, Equatable {
var id = UUID()
var name: String
var description: String
var timesCompleted: Int
}

Activities Class:

class Activities: ObservableObject {
@Published var activityList = [Activity]() {
    didSet {
        if let encoded = try? JSONEncoder().encode(activityList) {
            UserDefaults.standard.set(encoded, forKey: "activityList")
        }
    }
}

init() {
    if let savedList = UserDefaults.standard.data(forKey: "activityList") {
        if let decodedList = try? JSONDecoder().decode([Activity].self, from: savedList) {
            activityList = decodedList
            return
        }
    }
    activityList = []
}

init(activityList: [Activity]) {
    self.activityList = activityList
}

subscript(index: Int) -> Activity {
    get {
        assert(index < activityList.count, "Index out of range")
        return activityList[index]
    }

    set {
        assert(index < activityList.count, "Index out of range")
        activityList[index] = newValue
    }
}
}

ContentView:

struct ContentView: View {
@StateObject var activities = Activities()
@State private var showingAddActivity = false

var body: some View {
    NavigationView {
        List {
            ForEach(activities.activityList) { activity in
                NavigationLink {
                    ActivityDetailView(activity: activity, activities: activities)
                } label: {
                    Text(activity.name)
                }
            }
        }
        .navigationTitle("Habits")
        .toolbar {
            Button {
                showingAddActivity = true
                let _ = print("add activity")
            }
        label: {
            Image(systemName: "plus")
        }
        }
    }
    .sheet(isPresented: $showingAddActivity) {
        AddActivityView(activities: activities)
    }
}
}

ActivityDetailView - This is where the problem is. As soon as I try to do anything other than append to activities.activityList this view crashes and returns to ContentView. You can see in updateTimesCompleted() a bunch of my different attempts which all fail.

struct ActivityDetailView: View {
@State private var timesCompleted = 0
let activity: Activity

@ObservedObject var activities: Activities

var body: some View {
    NavigationView {
        Form {
            Text("Activity: \(activity.name)")
            Text("Description: \(activity.description)")

            Stepper {
                Text("Times Completed: \(timesCompleted)")
            } onIncrement: {
                timesCompleted += 1
                updateTimesCompleted()
            } onDecrement: {
                if timesCompleted > 0 {
                    timesCompleted -= 1
                    updateTimesCompleted()
                }
            }
        }
        .navigationTitle("Activity Details")
    }
}

func updateTimesCompleted() {
    let newActivity = Activity(name: activity.name, description: activity.description, timesCompleted: timesCompleted)

    let _ = print("count: \(activities.activityList.count)")

    let index = activities.activityList.firstIndex(of: activity)
    let _ = print(index ?? -666)
    if let index = index {
        activities.activityList[index] = Activity(name: activity.name, description: activity.description, timesCompleted: timesCompleted)

        //activities.activityList.swapAt(index, activities.activityList.count - 1)
        //activities.activityList[index].incrementTimesCompleted()
        //activities.activityList.append(newActivity)
        //activities.activityList.remove(at: index)
        //activities.activityList.removeAll()
        //activities.activityList.append(newActivity)
    }
}
}

AddActivityView - This works fine, but this is consistent with what I'm experiencing in ActivityDetailView as it only uses append and append is the only thing that works.

struct AddActivityView: View {
    @State private var activityName = ""
    @State private var activityDescription = ""

    @ObservedObject var activities: Activities

    @Environment(\.dismiss) var dismiss

    var body: some View {
        NavigationView {
            Form {
                VStack {
                    TextField("Name", text: $activityName)
                    TextField("Description", text: $activityDescription)
                }
            }
            .navigationTitle("Add Activity")
            .toolbar {
                Button("Save") {
                    let activity = Activity(name: activityName, description: activityDescription, timesCompleted: 0)
                    activities.activityList.append(activity)

                    dismiss()
                }
            }
        }
    }
}

struct AddActivityView_Previews: PreviewProvider {
    static var previews: some View {
        AddActivityView(activities: Activities(activityList: [Activity(name: "Example", description: "Ex Desc", timesCompleted: 0)]))
    }
}

I'm copying this from another thread so the solution is present here also.

Got some help in r/iosprogramming. I think the hints for the challenge are perhaps out of date and misleading based on this article which explained how to do it: https://www.swiftbysundell.com/articles/bindable-swiftui-list-elements/

You don't even have to pass the class holding the collection to the view or mess around with indices.

Here's the solution:

struct ContentView: View {
    @StateObject var activities = Activities()
    @State private var showingAddActivity = false

    var body: some View {
        NavigationView {
            List {
                ForEach($activities.activityList) { $activity in  //This line is key
                    NavigationLink {
                        ActivityDetailView(activity: $activity)  //So is this
                    } label: {
                        Text(activity.name)
                    }
                }
            }
            .navigationTitle("Habits")
            .toolbar {
                Button {
                    showingAddActivity = true
                }
            label: {
                Image(systemName: "plus")
            }
            }
        }
        .sheet(isPresented: $showingAddActivity) {
            AddActivityView(activities: activities)
        }
    }
}

struct ActivityDetailView: View {
    @Binding var activity: Activity //Now with @Binding we can modify the array element directly

    var body: some View {
        NavigationView {
            Form {
                Text("Activity: \(activity.name)")
                Text("Description: \(activity.description)")

                Stepper {
                    Text("Times Completed: \(activity.timesCompleted)")
                } onIncrement: {
                    activity.timesCompleted += 1
                } onDecrement: {
                    if activity.timesCompleted > 0 {
                        activity.timesCompleted -= 1
                    }
                }
            }
            .navigationTitle("Activity Details")
        }
    }
}