Previewing ContentView with CoreData

Question

When I try to a SwiftUI ContentView that contains a CoreData fetch request, the preview crashes. Wondering what the correct way to setup the @environment so the preview can access the coredata stack. This works fine when building to a simulator but not with a PreviewProvider

import SwiftUI

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

    @FetchRequest(entity: ProgrammingLanguage.entity(), sortDescriptors: [
            NSSortDescriptor(keyPath: \ProgrammingLanguage.name, ascending: true),
            NSSortDescriptor(keyPath: \ProgrammingLanguage.creator, ascending: false)
        ]) var languages: FetchedResults<ProgrammingLanguage>

    var body: some View {
        NavigationView {
            List {
                ForEach(languages, id: \.self) { language in
                    Text("Language: \(language.name ?? "Anonymous")")
                }
            }
            .navigationBarTitle("My Languages")
        }
    }
}

struct ContentView_Previews: PreviewProvider {
    static var previews: some View {
        ContentView()
    }
}

When I try to pass in argument to the ContentView in ContentView_Previews like so I get the following compiler error.

ContentView(managedObjectContext: managedObjectContext)

Error: Instance member 'managedObjectContext' cannot be used on type 'ContentView_Previews'

Maybe this isn't supported by SwiftUI previews yet? Or is there anything that could fix this?

I'm running Xcode 11 Beta 7.

Answer 1

Credit goes to @ShadowDES - in the Master/Detail template project in Xcode Beta 7 there's a preview that uses Core Data:

#if DEBUG
struct ContentView_Previews: PreviewProvider {
    static var previews: some View {
        let context = (UIApplication.shared.delegate as! AppDelegate).persistentContainer.viewContext
        return ContentView().environment(\.managedObjectContext, context)
    }
}
#endif

This works for me in Xcode Beta 5 (my Beta 7 crashes)