ContentView.swift

struct ContentView: View {
    @Environment(\.managedObjectContext) var context
    @State private var isShowingModal = false

    var body: some View {
        Button(action: {
            self.isShowingModal.toggle()
        }) {
            Text("go to SubView")
        }.sheet(isPresented: $isShowingModal) {
            SubView().environment(\.managedObjectContext, self.context)
        }
    }
}