immutable_example.dart

import 'package:flutter/material.dart';

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

@immutable
class UserProfile {
  final String name;
  final List<String> friends;

  UserProfile(this.name, this.friends);

  UserProfile addFriend(String friendId) {
    return UserProfile(name, List.from(friends)..add(friendId));
  }

  UserProfile removeLastFriend() {
    if (friends.isEmpty) return this;
    return UserProfile(name, List.from(friends)..removeLast());
  }
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: HomeScreen(),
    );
  }
}

class HomeScreen extends StatefulWidget {
  @override
  _HomeScreenState createState() => _HomeScreenState();
}

class _HomeScreenState extends State<HomeScreen> {
  UserProfile userProfile = UserProfile('John Doe', []);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: Text('Immutable State Demo')),
      body: Column(
        children: [
          // Displaying friends
          Expanded(
            child: ListView.builder(
              itemCount: userProfile.friends.length,
              itemBuilder: (context, index) {
                return ListTile(
                  title: Text(userProfile.friends[index]),
                );
              },
            ),
          ),
          // Button to add a friend
          ElevatedButton(
            child: Text('Add Friend'),
            onPressed: () {
              setState(() {
                userProfile = userProfile.addFriend('Friend ${userProfile.friends.length + 1}');
              });
            },
          ),
          // Button to remove the last friend using immutable operation
          ElevatedButton(
            child: Text('Remove Last Friend'),
            onPressed: () {
              setState(() {
                userProfile = userProfile.removeLastFriend();
              });
            },
          ),
        ],
      ),
    );
  }
}