SwiftUI: update a specific object value in a @State array and see changes on screen

I'm still fairly new at Swift and I cannot seem to get the value (points) to update on the screen. ScenarioToken is a CoreData entity.
I have tried a few things but seem to be stuck. I have a variable in my view:

@State private var scenarioTokens: [ScenarioToken]

and I display all the elements:

ForEach ($scenarioTokens) {$scenarioToken in
    HStack {
        if let $token = scenarioToken.token {                                  
            Text("\($token.label ?? "")")
                                
            Spacer()

            Button{
                increasePoints(scenarioToken: scenarioToken)
            } label: {
               Image(systemName: "plus.square")
            }
            .frame(width: 25)
            .buttonStyle(BorderlessButtonStyle())

            Text("\(scenarioToken.points)")
               .frame(width: 25, alignment: .trailing)

            Button{
                decreasePoints(scenarioToken: scenarioToken)
            } label: {
                Image(systemName: "minus.square")
            }
            .buttonStyle(BorderlessButtonStyle())
            .frame(width: 25)
        }
    }
}

The two functions I am calling are:

func increasePoints(scenarioToken: ScenarioToken) {
    guard let sign = scenarioToken.token?.sign else {
        return
    }
    scenarioToken.points+=1
}

func decreasePoints(scenarioToken: ScenarioToken) {
    guard let sign = scenarioToken.token?.sign else {
        return
    }
    scenarioToken.points-=1
}

I an article on Bindable SwiftUI list elements which seemed to indicate I could iterate over a state object. There was another post on Hacking With Swift, but it was more about viewing the information in an array in a view using @Binding.

If I change the line from:

Text("\(scenarioToken.points)")

to:

Text("\($scenarioToken.points)")

I get this error:

> No exact matches in call to instance method 'appendInterpolation'

I am trying to build an array of [ScenarioToken], which is a many to many between Scenario and Token with an additional points attribute. I want the user to be able to add/edit a complete Scenario detail view, adding Tokens and applying points, and allow them to cancel without disrupting the data in Core Data, or save/update with all the changes.

I did research this topic and found little on many to many joins like this (with additional attributes). I tried to keep the scope concise for this question to the specific problem I was having in implementing it, which is down to the updating of the points.

All the videos I've seen:

• Swift Arcade basic 101 w/no update screens, uses alerts, is not many to many.
• Sam Meech-Ward good video but no edit screen and is one to many
• Stewart Lynch this is a really good series by Stewart and comes really close to answering my question, but does not include a many to many
• Paul Hudson great examples always, but not many to many and there is no edit/update of the review.
• CodeWithChris another good example but not many to many or saving/storing a complete list of items all at once.
• Swiftful Thinking again, great content, but shows how one to many relationships work in Core Data but not really in the context of an app or many/many with more complex scenarios.

I found the problem. When you have many:many relationships and are trying to edit an attribute on the relationship, it's actually a nested observable object, which does not trigger the information in the view to change. It was outlined in this post Nested Observable Objects in SwiftUI.

I had already gone down the road of creating a separate object for holding the relationship information, which had the same problem, but I created a subview for it as the article recommended, and the data changes were visible.

If you want to update UI with your Model changes then you have to use ObservableObject model and ObserverdObject variable for the same.

ObservableObject Model:

class ScenarioToeknList : ObservableObject{
    static let shared = ScenarioToeknList()
    @Published var scenarioTokens = [ScenarioToken]()
}

In your view make ObservedObject like this:

@ObservedObject var objScenarioTokens : ScenarioToeknList = ScenarioToeknList.shared

Now access the array of token using ObservedObject variable so you can update your view with model changes.