main.dart

import 'dart:async';

import 'package:flutter/material.dart';

void main() => runApp(const MyApp());

class MyApp extends StatelessWidget {
  const MyApp({super.key});

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      debugShowCheckedModeBanner: false,
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: const MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatelessWidget {
  const MyHomePage({
    super.key,
    required this.title,
  });
  final String title;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(title),
      ),
      body: Center(
        child: OutlinedButton(
          onPressed: () async {
            final result = await progress(
              context: context,
              title: Text('Processing...'),
              result: _process(),
            );

            print('Result is $result');
          },
          child: const Text('Process'),
        ),
      ),
    );
  }

  Future<int> _process() async {
    await Future.delayed(const Duration(seconds: 2));
    return 42;
  }
}

Future<T?> progress<T>({
  required BuildContext context,
  required Future<T> result,
  required Widget title,
}) async {
  print('Processing...');
  final answer = await result;
  print('done.');
  return answer;
}