Show error message

home_screen_manager.dart

class HomeScreenManager {
  void Function(String message)? onError;

  Future<void> trySomething() async {
    await Future.delayed(const Duration(milliseconds: 200));
    onError?.call('Sorry, there was an error.');
  }
}

main.dart

import 'package:flutter/material.dart';
import 'home_screen_manager.dart';

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

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

  @override
  Widget build(BuildContext context) {
    return const MaterialApp(
      home: HomeScreen(),
    );
  }
}

class HomeScreen extends StatefulWidget {
  const HomeScreen({super.key});

  @override
  State<HomeScreen> createState() => _HomeScreenState();
}

class _HomeScreenState extends State<HomeScreen> {
  final manager = HomeScreenManager();

  void _showDialog(String errorMessage) {
    final alert = AlertDialog(
      content: Text(
        errorMessage,
        style: const TextStyle(color: Colors.red),
      ),
    );
    showDialog(
      context: context,
      builder: (BuildContext context) {
        return alert;
      },
    );
  }

  void _showSnackbar(String errorMessage) {
    final snackBar = SnackBar(
      content: Text(
        errorMessage,
        style: const TextStyle(color: Colors.red),
      ),
    );
    ScaffoldMessenger.of(context).showSnackBar(snackBar);
  }

  @override
  void initState() {
    super.initState();
    // manager.onError = _showDialog;
    manager.onError = _showSnackbar;
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
        child: ElevatedButton(
          onPressed: manager.trySomething,
          child: const Text('Try to do something'),
        ),
      ),
    );
  }
}