ForEach NavigationLink with State and Binding

Question

I'm trying to generate a ForEach with a NavigationLink and use State and Binding to pass some entity around:

struct ContentView: View {
    @Environment(\.managedObjectContext) var moc

    @FetchRequest(
        entity: MyEntity.entity(),
        sortDescriptors: [
            NSSortDescriptor(keyPath: \MyEntity.name, ascending: true)
        ]

    ) var entries: FetchedResults<MyEntity>

    var body: some View {
        NavigationView {
            List {
                ForEach(entries, id: \.self) { (entry: MyEntity) in
                    NavigationLink(destination: DetailView(myEntry: $entry)) {
                        Text(entry.name!)
                    }
                }.
            }
        }
    }
}

And then the following view:

struct DetailView: View {
    @Binding var myEntry: MyEntity

    var body: some View {
        Text(myEntry.name!)
    }
}

The problem is I can not pass the value to Detail view since the error:

Use of unresolved identifier '$entry'

What is wrong here and how to solve this?

If I just have a simple @State its no problem to pass it via the binding, but I want/need to use it in the ForEach for the FetchedResults

EDIT: If I remove the $ I get Cannot convert value of type 'MyEntity' to expected argument type 'Binding<MyEntity>'

EDIT2: The purpose is to pass some object to DetailView and then pass it back later to ContentView

check the type of entry which is provided in initialization closure by ForEach. Does MyEntity type provided its binding via its projectedValue property? That is what $ in front of entry means. — user3441734, Feb 23 '20 at 11:25
If I remove the $ I get: Cannot convert value of type 'MyEntity' to expected argument type 'Binding' — gurehbgui, Feb 23 '20 at 11:29
thats because you define it as parameter of DetailView. But MyEntity is not Binding. with $entity compiler complain, because it doesn't exists. $ is shortcut to projectedValue, see property wrappers definition — user3441734, Feb 23 '20 at 11:34
So what I need to to since I not only need it in DetailView but I also need to pass is back later to ContentView — gurehbgui, Feb 23 '20 at 11:36
it is some reference type, so you can modify it, if you like. — user3441734, Feb 23 '20 at 11:42

score 2 · Accepted Answer · answered Feb 23 '20 at 12:06

Use the following in ForEach

   ForEach(entries, id: \.self) { entry in
        NavigationLink(destination: DetailView(myEntry: entry)) {
            Text(entry.name!)
        }
    }

and the following in DetailView

struct DetailView: View {
    var myEntry: MyEntity

    var body: some View {
        Text(myEntry.name!)
    }
}

The MyEntity is class, so you pass object by reference and changing it in DetailView you change same object.

score 1 · Answer 2 · answered Feb 23 '20 at 17:06

FetchedResults<MyEntity> entities does not conform to Binding or DynamicProperty. For the $ symbol to workout must conform to Binding.

You can make a FetchedResultsController in an ObservableObject to get the same functionality as an @FetchRequestand have the ability to pass the values in an EnvironmentObject or ObservedObject.

ForEach NavigationLink with State and Binding

2 Answers2