flutter

name	flutter
description	Flutter cross-platform UI toolkit with Dart. Use for mobile/web/desktop.

Flutter

Flutter is Google's UI toolkit for building natively compiled applications for mobile, web, and desktop from a single codebase. It uses the Dart programming language and the Skia/Impeller graphics engine to render high-performance, pixel-perfect UIs.

When to Use

• Building high-performance Android and iOS apps with a single codebase.
• Creating custom, branded UI designs that need to look identical across platforms.
• Developing prototypes or MVPs quickly with Hot Reload.
• needing a solution that compiles to native code (ARM/x86) and WebAssembly.

Quick Start

// main.dart
import 'package:flutter/material.dart';
import 'package:flutter_bloc/flutter_bloc.dart';
import 'package:go_router/go_router.dart';

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

// Router configuration
final _router = GoRouter(
  routes: [
    GoRoute(
      path: '/',
      builder: (context, state) => const HomePage(),
    ),
  ],
);

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

  @override
  Widget build(BuildContext context) {
    return BlocProvider(
      create: (_) => CounterCubit(),
      child: MaterialApp.router(
        routerConfig: _router,
        theme: ThemeData(useMaterial3: true, colorSchemeSeed: Colors.blue),
      ),
    );
  }
}

// Bloc/Cubit Logic
class CounterCubit extends Cubit<int> {
  CounterCubit() : super(0);

  void increment() => emit(state + 1);
}

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

  @override
  Widget build(BuildContext context) {
    // Access state via context.read/watch or BlocBuilder
    final count = context.select((CounterCubit cubit) => cubit.state);

    return Scaffold(
      appBar: AppBar(title: const Text('Flutter & Bloc')),
      body: Center(
        child: Text(
          'Count: $count',
          style: Theme.of(context).textTheme.headlineMedium,
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: () => context.read<CounterCubit>().increment(),
        child: const Icon(Icons.add),
      ),
    );
  }
}

Core Concepts

Widget Tree & Element Tree

Flutter uses a reactive style where the UI is built from a tree of immutable Widgets.

• Widget: A configuration for an Element. Immutable description of part of the UI.
• Element: An instantiation of a Widget at a particular location in the tree. Mutable manager of state and lifecycle.
• RenderObject: The actual object that gets painted on the screen.

State Management (Bloc)

Modern Flutter apps often use the Bloc (Business Logic Component) pattern for separation of concerns and predictable state.

• Events: Inputs to the Bloc (e.g., button pressed).
• States: Outputs from the Bloc (e.g., loading, data loaded).
• Bloc/Cubit: The class that receives events and emits new states.
• BlocBuilder: Widget that rebuilds in response to new states.

Asynchronous Programming (Isolates)

Dart is single-threaded but event-driven. Heavy computations should be moved to background Isolates to avoid blocking the UI thread (jank).

Common Patterns

Feature-First Architecture

Organize files by feature rather than by layer.

lib/
  src/
    features/
      auth/
        data/
        domain/
        presentation/
          bloc/
          views/
      products/
    shared/
      components/
      constants/
    app.dart
    main.dart

Clean Architecture with Repositories

• Data Layer: Repositories, API clients (Dio/Http), DTOs.
• Domain Layer: Entities, business logic (pure Dart).
• Presentation Layer: Widgets, Blocs/Cubits.

Best Practices

Do:

• Use const constructors everywhere possible to optimize rebuilds.
• Use GoRouter for deep linking and declarative navigation.
• Use flutter_bloc to separate business logic from UI.
• Use ThemeData and TextTheme for consistent styling.

Don't:

• Don't put complex logic inside build() methods.
• Don't misuse setState for complex global state.
• Don't block the main thread; use compute() for heavy JSON parsing or calculations.

Troubleshooting

| Error | Cause | Solution | 140: | :--------------------------------------------- | :--------------------------------------------- | :----------------------------------------------------------- | 141: | RenderFlex overflowed by ... pixels | Content is too wide/tall for the parent. | Wrap in Expanded, Flexible, or SingleChildScrollView. | 142: | ProviderNotFoundException | Reading a Bloc without a provider up the tree. | Ensure BlocProvider wraps the widget trying to access it. | 143: | LateInitializationError | Accessing a late variable before assignment. | Ensure generic initialization or use nullable types locally. | 144: | Vertical viewport was given unbounded height | ListView inside Column without constraints. | Wrap ListView in Expanded or SizedBox. |

References

• Official Flutter Docs
• Bloc Library Documentation
• Flutter Engineering