main.dart

import 'package:flutter/material.dart';

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

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

class HomePage extends StatefulWidget {
  const HomePage({Key? key}) : super(key: key);

  @override
  State<HomePage> createState() => HomePageState();
}

class HomePageState extends State<HomePage> {
  final mainKey = GlobalKey();
  final servicesKey = GlobalKey();
  final portfolioKey = GlobalKey();

  Widget build(BuildContext context) {
    return MaterialApp(
        theme: ThemeData.dark().copyWith(
          scaffoldBackgroundColor: darkBlue,
        ),
        debugShowCheckedModeBanner: false,
        home: Scaffold(
          appBar: AppBar(actions: [
            ElevatedButton(
              onPressed: () {
                Scrollable.ensureVisible(portfolioKey.currentContext!);
              },
              child: const Text('Scroll To Portfolio',
                  style: TextStyle(color: Colors.yellow)),
            ),
          ]),
          body: SingleChildScrollView(
            child: Column(children: [
              MainSection(key: mainKey),
              ServicesSection(key: servicesKey),
              PortfolioSection(key: portfolioKey, mainSectionKey: mainKey),
            ]),
          ),
        ));
  }
}

class MainSection extends StatefulWidget {
  const MainSection({Key? key}) : super(key: key);

  @override
  State<MainSection> createState() => MainSectionState();
}

class MainSectionState extends State<MainSection> {
  @override
  Widget build(BuildContext context) {
    return Container(
        height: 800,
        width: double.infinity,
        color: Colors.blue,
        child: Text(
          'Hello, Main!',
          style: Theme.of(context).textTheme.headline4,
        ));
  }
}

class ServicesSection extends StatefulWidget {
  const ServicesSection({Key? key}) : super(key: key);

  @override
  State<ServicesSection> createState() => _ServicesSectionState();
}

class _ServicesSectionState extends State<ServicesSection> {
  @override
  Widget build(BuildContext context) {
    return Container(
        height: 800,
        width: double.infinity,
        color: Colors.red,
        child: Text(
          'Hello, Services!',
          style: Theme.of(context).textTheme.headline4,
        ));
  }
}

class PortfolioSection extends StatefulWidget {
  const PortfolioSection({Key? key, required this.mainSectionKey}) : super(key: key);
  final GlobalKey mainSectionKey;
  @override
  State<PortfolioSection> createState() => _PortfolioSectionState();
}

class _PortfolioSectionState extends State<PortfolioSection> {

  @override
  Widget build(BuildContext context) {
    return Container(
      height: 650,
      width: double.infinity,
      color: Colors.green,
      child: Column(
        children: [
          Expanded(child: Text('Portfolio Section')),
          ElevatedButton(
            onPressed: () {
              // i want to scroll to MainSection when pressing the button but 
              // in my flutter project im getting "null Expression called on a null value" error
              // for the "_globalKey.currentContext!" call
              
              Scrollable.ensureVisible(widget.mainSectionKey.currentContext!);
            },
            child: Text('Scroll To Main!'),
          )
        ],
      ),
    );
  }
}