class CounterPage extends StatefulWidget { @override _CounterPageState createState() => _CounterPageState(); }  class _CounterPageState extends State<CounterPage> { int _counter = 0;  void _incrementCounter() { setState(() { _counter++; }); }  @override Widget build(BuildContext context) { return Scaffold( appBar: AppBar(title: Text('Counter')), body: Center( child: Text( 'Count: $_counter', style: TextStyle(fontSize: 24), ), ), floatingActionButton: FloatingActionButton( onPressed: _incrementCounter, child: Icon(Icons.add), ), ); } }

class CounterProvider extends InheritedWidget { final int counter; final Function incrementCounter;  CounterProvider({ Key? key, required this.counter, required this.incrementCounter, required Widget child, }) : super(key: key, child: child);  static CounterProvider of(BuildContext context) { return context.dependOnInheritedWidgetOfExactType<CounterProvider>()!; }  @override bool updateShouldNotify(CounterProvider oldWidget) { return counter != oldWidget.counter; } }  // Usage class MyApp extends StatefulWidget { @override _MyAppState createState() => _MyAppState(); }  class _MyAppState extends State<MyApp> { int _counter = 0;  void _incrementCounter() { setState(() { _counter++; }); }  @override Widget build(BuildContext context) { return CounterProvider( counter: _counter, incrementCounter: _incrementCounter, child: MaterialApp( home: CounterPage(), ), ); } }  class CounterPage extends StatelessWidget { @override Widget build(BuildContext context) { final provider = CounterProvider.of(context);  return Scaffold( appBar: AppBar(title: Text('Counter')), body: Center( child: Text( 'Count: ${provider.counter}', style: TextStyle(fontSize: 24), ), ), floatingActionButton: FloatingActionButton( onPressed: () => provider.incrementCounter(), child: Icon(Icons.add), ), ); } }

// First, add the provider package to your pubspec.yaml // dependencies: //   provider: ^6.0.5  import 'package:flutter/material.dart'; import 'package:provider/provider.dart';  // Create a model class class CounterModel extends ChangeNotifier { int _counter = 0;  int get counter => _counter;  void increment() { _counter++; notifyListeners();  // Notify listeners to rebuild } }  // Set up the provider void main() { runApp( ChangeNotifierProvider( create: (context) => CounterModel(), child: MyApp(), ), ); }  // Use the provider in your widgets class CounterPage extends StatelessWidget { @override Widget build(BuildContext context) { return Scaffold( appBar: AppBar(title: Text('Counter with Provider')), body: Center( child: Consumer<CounterModel>( builder: (context, model, child) { return Text( 'Count: ${model.counter}', style: TextStyle(fontSize: 24), ); }, ), ), floatingActionButton: FloatingActionButton( onPressed: () { // Access the model and call increment Provider.of<CounterModel>(context, listen: false).increment(); }, child: Icon(Icons.add), ), ); } }

// Navigate to a new screen Navigator.push( context, MaterialPageRoute(builder: (context) => SecondScreen()), );  // Go back to the previous screen Navigator.pop(context);  // Replace the current screen Navigator.pushReplacement( context, MaterialPageRoute(builder: (context) => ReplacementScreen()), );  // Clear the navigation stack and show a new screen Navigator.pushAndRemoveUntil( context, MaterialPageRoute(builder: (context) => HomeScreen()), (route) => false,  // Remove all previous routes );

void main() { runApp( MaterialApp( initialRoute: '/', routes: { '/': (context) => HomeScreen(), '/details': (context) => DetailsScreen(), '/settings': (context) => SettingsScreen(), }, ), ); }  // Navigate to a named route Navigator.pushNamed(context, '/details');  // Navigate with arguments Navigator.pushNamed( context, '/details', arguments: {'id': 123, 'title': 'Item Details'}, );  // Retrieve arguments in the destination screen final args = ModalRoute.of(context)!.settings.arguments as Map<String, dynamic>;

// Basic ListView with fixed children ListView( children: [ ListTile(title: Text('Item 1')), ListTile(title: Text('Item 2')), ListTile(title: Text('Item 3')), ], );  // ListView.builder for dynamic lists ListView.builder( itemCount: items.length, itemBuilder: (context, index) { return ListTile( title: Text(items[index].title), subtitle: Text(items[index].description), onTap: () { // Handle item tap }, ); }, );  // ListView.separated for lists with separators ListView.separated( itemCount: items.length, itemBuilder: (context, index) { return ListTile(title: Text(items[index])); }, separatorBuilder: (context, index) { return Divider();  // Add a divider between items }, );

// Basic GridView with fixed children GridView.count( crossAxisCount: 2,  // 2 columns children: [ Card(child: Center(child: Text('Item 1'))), Card(child: Center(child: Text('Item 2'))), Card(child: Center(child: Text('Item 3'))), Card(child: Center(child: Text('Item 4'))), ], );  // GridView.builder for dynamic grids GridView.builder( gridDelegate: SliverGridDelegateWithFixedCrossAxisCount( crossAxisCount: 2, crossAxisSpacing: 10, mainAxisSpacing: 10, ), itemCount: items.length, itemBuilder: (context, index) { return Card( child: Center( child: Text(items[index]), ), ); }, );

// Creating a Future Future<String> fetchData() async { // Simulate network request await Future.delayed(Duration(seconds: 2)); return 'Data loaded successfully'; }  // Using a Future void loadData() async { try { String result = await fetchData(); print(result);  // Prints: Data loaded successfully } catch (e) { print('Error: $e'); } }  // Alternative syntax using then/catchError fetchData() .then((result) => print(result)) .catchError((error) => print('Error: $error'));

FutureBuilder<String>( future: fetchData(), builder: (context, snapshot) { if (snapshot.connectionState == ConnectionState.waiting) { return CircularProgressIndicator();  // Loading indicator } else if (snapshot.hasError) { return Text('Error: ${snapshot.error}');  // Error state } else { return Text(snapshot.data!);  // Success state } }, )

// Creating a Stream Stream<int> countStream(int max) async* { for (int i = 1; i <= max; i++) { await Future.delayed(Duration(seconds: 1)); yield i;  // Emit a value to the stream } }  // Using a Stream void listenToStream() { final stream = countStream(5);  stream.listen( (data) => print('Data: $data'),  // Called for each emitted value onError: (error) => print('Error: $error'), onDone: () => print('Stream completed'), ); }  // StreamBuilder for UI StreamBuilder<int>( stream: countStream(5), builder: (context, snapshot) { if (snapshot.connectionState == ConnectionState.waiting) { return CircularProgressIndicator(); } else if (snapshot.hasError) { return Text('Error: ${snapshot.error}'); } else if (snapshot.hasData) { return Text('Count: ${snapshot.data}'); } else { return Text('No data'); } }, )

// Create a Form with a GlobalKey final _formKey = GlobalKey<FormState>();  Form( key: _formKey, child: Column( children: [ TextFormField( decoration: InputDecoration(labelText: 'Email'), validator: (value) { if (value == null || value.isEmpty) { return 'Please enter your email'; } if (!value.contains('@')) { return 'Please enter a valid email'; } return null;  // Return null for valid input }, ), TextFormField( decoration: InputDecoration(labelText: 'Password'), obscureText: true,  // Hide password validator: (value) { if (value == null || value.isEmpty) { return 'Please enter your password'; } if (value.length < 6) { return 'Password must be at least 6 characters'; } return null; }, ), ElevatedButton( onPressed: () { // Validate the form if (_formKey.currentState!.validate()) { // Form is valid, process the data _formKey.currentState!.save(); // Submit the form } }, child: Text('Submit'), ), ], ), )

class MyFormState extends State<MyForm> { // Create controllers final _emailController = TextEditingController(); final _passwordController = TextEditingController();  @override void dispose() { // Clean up controllers when the widget is disposed _emailController.dispose(); _passwordController.dispose(); super.dispose(); }  @override Widget build(BuildContext context) { return Form( child: Column( children: [ TextFormField( controller: _emailController, decoration: InputDecoration(labelText: 'Email'), ), TextFormField( controller: _passwordController, decoration: InputDecoration(labelText: 'Password'), obscureText: true, ), ElevatedButton( onPressed: () { // Access the values final email = _emailController.text; final password = _passwordController.text; print('Email: $email, Password: $password'); }, child: Text('Submit'), ), ], ), ); } }