Previewing ContentView with CoreData : <p>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</p>

<pre><code>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&lt;ProgrammingLanguage&gt;

    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()
    }
}
</code></pre>

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

<pre><code>ContentView(managedObjectContext: managedObjectContext)
</code></pre>

<p>Error: Instance member 'managedObjectContext' cannot be used on type 'ContentView_Previews'</p>

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

<p>I'm running Xcode 11 Beta 7.</p>
