SwiftUI Build List from Core Data One-to-Many Set

Question

I'm trying to build a SwiftUI view with data from Core Data. One of the entities has a one-to-many relationship with another entity. I have a basic master detail type with a NavigationLink to a second view which should be the equivalent of a detail view. I can in fact list all of the details for the second entity except for the Set of related objects.

Relevant entities:

public class Regimen : NSManagedObject, Identifiable {
    @NSManaged public var id: UUID
    @NSManaged public var name: String?
    //...more

    @NSManaged public var drugObjects: Set<DrugObject>
}

public class DrugObject : NSManagedObject, Identifiable {
    @NSManaged public var id: UUID
    @NSManaged public var name: String?
    //...more

    @NSManaged public var regimen: Regimen
}

The master list:

struct RegimenListView: View {
    @Environment(\.managedObjectContext) var managedObjectContext
    @FetchRequest(fetchRequest: Regimen.getAllRegimens()) var myRegimens
    var body: some View {
        NavigationView {
            List {
                ForEach(myRegimens, id: \.self) { mr in
                    NavigationLink(destination: RegimenDetailView(regimen: mr)) {
                        Text(mr.name ?? "no regimen name")
                    }
                }
            }.navigationBarTitle("Regimens")
        }
    }
}

The detail list:

struct RegimenDetailView: View {
    var regimen: Regimen
    var body: some View {
        //let da: [DrugObject] = Array(regimen.drugObjects)
        return NavigationView {
            VStack {
                Text(regimen.name ?? "no regimen name")
                List {
                    ForEach(regimen.drugObjects, id: \.self) { x in
                        Text(x.name ?? "no drugObject name")
                    }
                }
            }
        }
    }
}

If I try to build as listed above, I get an error on the ForEach line: Generic struct 'ForEach' requires that 'Set' conform to 'RandomAccessCollection'

If I first try to convert to an Array, it blows up with the error: Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[MyChems.DrugObject copyWithZone:]: unrecognized selector sent to instance '

Any guidance would be appreciated. Xcode 11.6 iOS 13.6

Asperi Asperi · Accepted Answer · 2020-07-24T04:51:49

Try to add

extension DragObject: NSCopying {
    func copy(with zone: NSZone? = nil) -> Any {
        return self
    }
}

and use

List {
    ForEach(Array(regimen.drugObjects), id: \.self) { x in
        Text(x.name ?? "no drugObject name")
    }
}

SwiftUI Build List from Core Data One-to-Many Set

1 Answers