FutureProvider and StreamProviderFutureProvider و StreamProvider

class User {
  const User({required this.id, required this.name});

  final int id;
  final String name;
}

class Todo {
  const Todo({required this.id, required this.title});

  final int id;
  final String title;
}

// The lecture's "service locator" holds services like these.
// They pretend to be a slow server: the data arrives later.
class UserDataService {
  Future<User> getUser(int id) async {
    await Future.delayed(const Duration(milliseconds: 500));
    return User(id: id, name: 'Shilan');
  }
}

class TodoDataService {
  // One answer, later: a Future.
  Future<List<Todo>> getTodoList() async {
    await Future.delayed(const Duration(seconds: 1));
    return const [
      Todo(id: 1, title: 'Read chapter 8'),
      Todo(id: 2, title: 'Revise for the quiz'),
      Todo(id: 3, title: 'Buy a notebook'),
    ];
  }

  // Many answers over time: a Stream. Each value is the whole new list.
  Stream<List<Todo>> watchTodoList() async* {
    var todos = <Todo>[];
    for (final title in ['Read chapter 8', 'Call Hana', 'Practise layouts']) {
      await Future.delayed(const Duration(seconds: 1));
      todos = [...todos, Todo(id: todos.length + 1, title: title)];
      yield todos;
    }
  }
}

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

import 'todo_services.dart';

Future<void> main() async {
  final user = await UserDataService().getUser(1); // sign-in finished
  runApp(buildApp(user));
}

Widget buildApp(User user) {
  // Only the User goes through Provider (dependency injection).
  return Provider<User>.value(
    value: user, // the object already exists, so .value is right
    child: const MaterialApp(home: TodoListScreen()),
  );
}

// The to-do list still uses a stateful widget and a FutureBuilder.
class TodoListScreen extends StatefulWidget {
  const TodoListScreen({super.key});

  @override
  State<TodoListScreen> createState() => _TodoListScreenState();
}

class _TodoListScreenState extends State<TodoListScreen> {
  late final Future<List<Todo>> _todos = TodoDataService().getTodoList();

  @override
  Widget build(BuildContext context) {
    final user = Provider.of<User>(context); // injected, not created here
    return Scaffold(
      appBar: AppBar(title: Text("${user.name}'s to-dos")),
      body: FutureBuilder<List<Todo>>(
        future: _todos,
        builder: (context, snapshot) {
          if (snapshot.connectionState != ConnectionState.done) {
            return const Center(child: CircularProgressIndicator());
          }
          if (snapshot.hasError) {
            return Center(child: Text('Error: ${snapshot.error}'));
          }
          final todos = snapshot.data!;
          return ListView.builder(
            itemCount: todos.length,
            itemBuilder: (context, i) => ListTile(title: Text(todos[i].title)),
          );
        },
      ),
    );
  }
}

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

import 'todo_services.dart';

Future<void> main() async {
  final user = await UserDataService().getUser(1);
  runApp(buildApp(user));
}

Widget buildApp(User user) {
  return MultiProvider(
    providers: [
      Provider<User>.value(value: user),
      FutureProvider<List<Todo>>(
        create: (_) => TodoDataService().getTodoList(),
        initialData: const [], // shown until the Future completes
      ),
    ],
    child: const MaterialApp(home: TodoListScreen()),
  );
}

// No State object and no FutureBuilder any more.
class TodoListScreen extends StatelessWidget {
  const TodoListScreen({super.key});

  @override
  Widget build(BuildContext context) {
    final user = context.watch<User>();
    final todos = context.watch<List<Todo>>(); // [] first, then the list
    return Scaffold(
      appBar: AppBar(title: Text("${user.name}'s to-dos")),
      body: ListView.builder(
        itemCount: todos.length,
        itemBuilder: (context, i) => ListTile(title: Text(todos[i].title)),
      ),
    );
  }
}

Widget buildApp() {
  return FutureProvider<List<Todo>?>(
    create: (_) => TodoDataService().getTodoList(),
    initialData: null, // null means "still loading"
    catchError: (_, error) => const [], // the Future failed: use an empty list
    child: const MaterialApp(home: TodoListScreen()),
  );
}

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

  @override
  Widget build(BuildContext context) {
    final todos = context.watch<List<Todo>?>(); // the same nullable type
    Widget body;
    if (todos == null) {
      body = const Center(child: CircularProgressIndicator()); // loading
    } else if (todos.isEmpty) {
      body = const Center(child: Text('No to-dos.'));
    } else {
      body = ListView(
        children: [for (final t in todos) ListTile(title: Text(t.title))],
      );
    }
    return Scaffold(appBar: AppBar(title: const Text('My to-dos')), body: body);
  }
}

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

import 'todo_services.dart';

void main() => runApp(buildApp(TodoDataService().watchTodoList()));

Widget buildApp(Stream<List<Todo>> todoStream) {
  return StreamProvider<List<Todo>>(
    create: (_) => todoStream,
    initialData: const [], // until the first list arrives
    child: const MaterialApp(home: LiveTodoScreen()),
  );
}

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

  @override
  Widget build(BuildContext context) {
    // Rebuilt every time the stream sends a new list.
    final todos = context.watch<List<Todo>>();
    return Scaffold(
      appBar: AppBar(title: Text('Live to-dos (${todos.length})')),
      body: todos.isEmpty
          ? const Center(child: Text('No to-dos yet.'))
          : ListView.builder(
              itemCount: todos.length,
              itemBuilder: (context, i) => ListTile(
                leading: CircleAvatar(child: Text('${todos[i].id}')),
                title: Text(todos[i].title),
              ),
            ),
    );
  }
}