Calling Navigator outside Widget build() gives context error - flutter

Question

So I'm basically trying to check if users have seen an Intro page in my flutter app. If they already have seen it, I want them to be directed to the Login() page. Else, I want them to be directed to the IntroScreen() page.
However, I am getting the following error: Unhandled Exception: Navigator operation requested with a context that does not include a Navigator. E/flutter (13982): The context used to push or pop routes from the Navigator must be that of a widget that is a descendant of a Navigator widget.
This is my code:
void main() => runApp(CheckSplash());
//check if the intro screen has already been seen
class CheckSplash extends StatefulWidget {
#override
_CheckSplashState createState() => _CheckSplashState();
}
class _CheckSplashState extends State<CheckSplash> {
bool _introseen=true;
Future checkIntroSeen() async {
SharedPreferences prefs = await SharedPreferences.getInstance();
bool _introseen = (prefs.getBool('seen') ?? false);
if (_introseen) {
Navigator.of(context).pushReplacement(
new MaterialPageRoute(builder: (BuildContext context) => Login()));
} else {
//await prefs.setBool('seen', true);
Navigator.of(context).pushReplacement(
new MaterialPageRoute(builder: (BuildContext context) => new IntroScreen()));
}
}
#override
void initState() {
super.initState();
new Timer(new Duration(milliseconds: 200), () {
checkIntroSeen();
});
}
#override
Widget build(BuildContext context) {
return MaterialApp(
theme: appTheme,
debugShowCheckedModeBanner: false,
home: Builder(
builder: (context) => Scaffold(
resizeToAvoidBottomPadding: false,
body: Center(child: CircularProgressIndicator(valueColor: new AlwaysStoppedAnimation<Color>(Colors.red[300])))
)
)
);
}
}

Answer 1

So I solved the problem by using the flutter GET library. Link: flutter get library
Using this library, one doesn't need the context to navigate between pages and thus it is a full proof method to navigate from anywhere in flutter.

Answer 2

I Have tried the easiest way. Create a function for your code after your contextBuilder. Then, Just put the context
as a function argument:
Widget build(BuildContext context) {
return ....(your code)
}
yourFunction(context) {
Navigator.pop(context);
Navigator.push(context, MaterialPageRoute(builder: (context) => LoginScreen()));
}
It is worked as expected for me. Thanks!

Answer 3

context inside initState is available inside SchedulerBinding.instance.addPostFrameCallback. This function fired after widget is built.
#override
void initState() {
super.initState();
SchedulerBinding.instance.addPostFrameCallback((_) {
new Timer(new Duration(milliseconds: 200), () {
checkIntroSeen();
});
});
}