[Projeto] Resolução do desafio

Obrigado @Leonardo Vieira Valério, sem a sua solução eu não teria conseguido. O title do AppBar ficou devendo ainda, porém deu preguiça.

import 'package:flutter/material.dart';
import 'package:nosso_primeiro_projeto/data/task_inherited.dart';

import '../components/task.dart';
import 'form_screen.dart';

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

  double nivelGlobal = 0;

  @override
  State<InitialScreen> createState() => _InitialScreenState();
}

class _InitialScreenState extends State<InitialScreen> {
  double calculaNivelGlobal() {
    double level = 0;
    for (Task task in TaskInherited.of(context).taskList) {
      level += (task.nivel / 10) * task.dificuldade;
    }
    return widget.nivelGlobal = level;
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        leading: Container(),
        title: Column(
          children: [
            Row(
              mainAxisAlignment: MainAxisAlignment.spaceBetween,
              children: [
                Text('Tarefas'),
                IconButton(
                    onPressed: () {
                      setState(() {
                        calculaNivelGlobal();
                      });
                    },
                    icon: const Icon(Icons.refresh)),
              ],
            ),
            Row(
              mainAxisAlignment: MainAxisAlignment.spaceBetween,
              crossAxisAlignment: CrossAxisAlignment.start,
              children: [
                SizedBox(
                  width: 200,
                  child: LinearProgressIndicator(
                    color: Colors.white,
                    value: widget.nivelGlobal / 10,
                  ),
                ),
                Text(
                  'Level: ${widget.nivelGlobal.toStringAsFixed(2)}',
                  style: const TextStyle(
                    fontSize: 12,
                  ),
                ),
              ],
            ),
          ],
        ),
      ),
      body: ListView(
        padding: const EdgeInsets.only(top: 8, bottom: 75),
        children: TaskInherited.of(context).taskList,
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: () {
          Navigator.push(
            context,
            MaterialPageRoute(
              builder: (contextNew) => FormScreen(
                //Precisou-se criar um novo contexto aqui
                taskContext: context,
              ),
            ),
          );
        },
        child: const Icon(Icons.add),
      ),
    );
  }
}