How to Access a Variable that is Associated with other Widget in Flutter?

main.dart

import 'package:flutter/material.dart';

final Color darkBlue = Color.fromARGB(255, 18, 32, 47);

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      theme: ThemeData.dark().copyWith(scaffoldBackgroundColor: darkBlue),
      debugShowCheckedModeBanner: false,
      home: Scaffold(
        body: Center(
          child: MyWidget(),
        ),
      ),
    );
  }
}

class MyWidget extends StatefulWidget {
  @override
  _MyWidgetState createState() => _MyWidgetState();
}

class _MyWidgetState extends State<MyWidget> {
  String _currentEmoji = 'my initial emoji';

  void _setEmoji() {
    // My Random Code Goes Here. (Never Mind)
    setState(() {
      _currentEmoji = 'new emoji';
    });
  }

  @override
  Widget build(BuildContext context) {
    return Column(children: [
      ElevatedButton(
        onPressed: _setEmoji,
        child: Text('press me'),
      ),
      Text(_currentEmoji),
    ]);
  }
}