How to navigate without context in flutter app?

I have an app that recieves push notification using OneSignal. I have made a notification opened handler that should open specific screen on click of the notification. How can i navigate to a screen without context. or how can I open specific screen on app startup. My code:

OneSignal.shared.setNotificationOpenedHandler((notification) {
  var notify = notification.notification.payload.additionalData;
  if (notify["type"] == "message") {
    Navigator.of(context).push(
      MaterialPageRoute(
        builder: (context) => DM(user: notify['id']),
      ),
    );
  }
  if (notify["type"] == "user") {
    Navigator.of(context).push(
      MaterialPageRoute(
        builder: (context) => Profileo(notify["id"]),
      ),
    );
  }
  if (notify["type"] == "post") {
    Navigator.of(context).push(
      MaterialPageRoute(
        builder: (context) => ViewPost(notify["id"]),
      ),
    );
  }
});

I am able to achieve this when the app is opened for the first time but It only opens the homepage If i close the app and even if I re-open it. I guess that is because the context is changed.

Please Help!!

Look at this here: https://github.com/brianegan/flutter_redux/issues/5#issuecomment-361215074

You can set a global key for your navigation:

final GlobalKey<NavigatorState> navigatorKey = GlobalKey<NavigatorState>();

Pass it to MaterialApp:

new MaterialApp(
      title: 'MyApp',
      onGenerateRoute: generateRoute,
      navigatorKey: navigatorKey,
    );

Push routes:

navigatorKey.currentState.pushNamed('/someRoute');

You can use this wonderful plugin: https://pub.dev/packages/get

Description from the package: A consistent navigation library that lets you navigate between screens, open dialogs, and display snackbars from anywhere in your code without context.

Get.to(NextScreen()); // look at this simplicity :)
Get.back(); //  pop()
Get.off(NextScreen()); // clears the previous routes and opens a new screen.