Having trouble updating passed variable in flutter

flutterprob.dart

class NavigationState extends State<MyNavigationHolder> {
  var goToPass = "/page1";
  
  assignPass(page) {
    print("inside assignPass");
    print("value of page: " + page);
    setState(() {goToPass = page;});
  }
  
  Widget build(BuildContext context) {
    return new Flexible(child: new HeaderPage(goTo: goToPass));
  }
}
  
  
  
import 'package:flutter/material.dart';
import 'main.dart';


class HeaderPage extends StatefulWidget {
  const HeaderPage({
    Key key,
    this.goTo
  }) : super(key: key);

  final String goTo;

  @override
  HeaderPageState createState() => new HeaderPageState();
}


class HeaderPageState extends State<HeaderPage> {
  HeaderPageState();
  
  @override
  Widget build(BuildContext context) {
    return new Text(widget.goTo);
  }
}