Flutter Cheatsheet

Flutter - Build Apps für alle Screen

Flutter ist das UI-Toolkit von Google, um schöne, native zusammengestellte Anwendungen für mobile, Web und Desktop von einer einzigen Codebasis zu erstellen. Es ist bekannt für seine expressive UI, schnelle Entwicklung Zyklus und native Leistung. < p>

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Inhaltsverzeichnis

• [Installation](LINK_0 -%20(LINK_0)
• Core Concepts
• (__LINK_0___)
• (__LINK_0___)
• [Navigation](LINK_0 -%20[State%20Management](_LINK_0 -%20[Networking](_LINK_0 -%20[Beständigkeit](LINK_0 -%20[Animations](_LINK_0 -%20[Platform%20Integration](_LINK_0 -%20Test
• [Debugging](_LINK_0__ -%20[Bestellung](_LINK_0___ -%20Beste%20Praktiken
• (__LINK_0___)

Installation

Flutter SDK

# Download Flutter SDK from https://flutter.dev/docs/get-started/install
# Extract the zip file

# Add Flutter to your path (for the current terminal session)
export PATH="$PATH:`pwd`/flutter/bin"

# Add Flutter to your path permanently (macOS/Linux)
echo 'export PATH="$PATH:[PATH_TO_FLUTTER_GIT_DIRECTORY]/flutter/bin"' >> ~/.zshrc
source ~/.zshrc

# Add Flutter to your path permanently (Windows)
# Update your system's environment variables
```_

### Aufbau der Plattform

#### Android Setup
```bash
# Install Android Studio
# Download from https://developer.android.com/studio

# Set up Android emulator
# Open Android Studio > AVD Manager > Create Virtual Device

# Accept Android licenses
flutter doctor --android-licenses
```_

#### iOS Setup (nur macOS)
```bash
# Install Xcode
# Download from Mac App Store

# Install CocoaPods
sudo gem install cocoapods

# Set up iOS simulator
open -a Simulator
```_

### Flutter Doktor
```bash
# Check your environment and see a report of the status of your Flutter installation
flutter doctor

# Verbose output
flutter doctor -v
```_

## Erste Schritte

### Neues Projekt erstellen
```bash
# Create a new Flutter project
flutter create my_app

# Navigate to the project directory
cd my_app

# Create a project with a specific organization
flutter create --org com.example my_app

# Create a project with a specific template
flutter create -t module my_module
```_

### Die App starten
```bash
# Run the app on an available device
flutter run

# Run on a specific device
flutter run -d chrome
flutter run -d 'iPhone 12'

# Run in release mode
flutter run --release

# Run with hot reload
# Press 'r' in the terminal

# Run with hot restart
# Press 'R' in the terminal
```_

### Projektstruktur

my_app/ ├── android/ # Android-specific code ├── ios/ # iOS-specific code ├── lib/ # Main Dart code │ ├── main.dart # App entry point │ ├── screens/ # Screen widgets │ ├── widgets/ # Reusable widgets │ ├── models/ # Data models │ ├── services/ # API services │ └── utils/ # Utility functions ├── test/ # Test files ├── pubspec.yaml # Project dependencies and metadata └── README.md # Project documentation ```_

Kernkonzepte

Dart Language Basics

```dart // Variables var name = 'Flutter'; String language = 'Dart'; int year = 2017; double version = 2.12; bool isAwesome = true;

// Functions int add(int a, int b) { return a + b; }

// Arrow syntax int multiply(int a, int b) => a * b;

// Classes class Person { String name; int age;

Person(this.name, this.age);

void sayHello() { print('Hello, my name is $name and I am $age years old.'); } }

// Asynchronous programming Future fetchData() async { await Future.delayed(Duration(seconds: 2)); return 'Data fetched'; }

void main() async { var person = Person('John Doe', 30); person.sayHello();

print('Fetching data...'); var data = await fetchData(); print(data); } ```_

Alles ist ein Widget

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

void main() { runApp( MaterialApp( home: Scaffold( appBar: AppBar( title: Text('My First Flutter App'), ), body: Center( child: Text('Hello, Flutter!'), ), ), ), ); } ```_

Erstellen von Kontexten

```dart // BuildContext provides information about the location of a widget in the widget tree. // It is used to access theme data, navigation, and other inherited widgets.

class MyWidget extends StatelessWidget { @override Widget build(BuildContext context) { return RaisedButton( onPressed: () { Scaffold.of(context).showSnackBar( SnackBar(content: Text('Button pressed')), ); }, child: Text('Press Me'), ); } } ```_

Stateless vs. Staatliche Widgets

```dart // StatelessWidget: A widget that does not require mutable state. class MyStatelessWidget extends StatelessWidget { final String title;

MyStatelessWidget({required this.title});

@override Widget build(BuildContext context) { return Text(title); } }

// StatefulWidget: A widget that has mutable state. class MyStatefulWidget extends StatefulWidget { @override _MyStatefulWidgetState createState() => _MyStatefulWidgetState(); }

class _MyStatefulWidgetState extends State { int _counter = 0;

void _incrementCounter() { setState(() { _counter++; }); }

@override Widget build(BuildContext context) { return Column( children: [ Text('Counter: $counter'), RaisedButton( onPressed: _incrementCounter, child: Text('Increment'), ), ], ); } } ```

Widgets

Basic Widgets

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

class BasicWidgets extends StatelessWidget { @override Widget build(BuildContext context) { return Scaffold( appBar: AppBar(title: Text('Basic Widgets')), body: SingleChildScrollView( padding: EdgeInsets.all(16.0), child: Column( crossAxisAlignment: CrossAxisAlignment.start, children: [ // Text Text('This is a Text widget', style: TextStyle(fontSize: 18)), SizedBox(height: 20),

        // Icon
        Icon(Icons.favorite, color: Colors.red, size: 30),
        SizedBox(height: 20),

        // Image
        Image.network('https://flutter.dev/images/flutter-logo-sharing.png'),
        SizedBox(height: 20),

        // Asset Image
        Image.asset('assets/images/logo.png'),
        SizedBox(height: 20),

        // Button
        RaisedButton(
          onPressed: () {},
          child: Text('RaisedButton'),
        ),
        SizedBox(height: 10),
        FlatButton(
          onPressed: () {},
          child: Text('FlatButton'),
        ),
        SizedBox(height: 10),
        IconButton(
          onPressed: () {},
          icon: Icon(Icons.thumb_up),
        ),
        SizedBox(height: 20),

        // TextField
        TextField(
          decoration: InputDecoration(
            labelText: 'Enter your name',
            border: OutlineInputBorder(),
          ),
        ),
        SizedBox(height: 20),

        // Checkbox
        CheckboxListTile(
          title: Text('Accept terms and conditions'),
          value: true,
          onChanged: (value) {},
        ),
        SizedBox(height: 20),

        // Radio
        RadioListTile(
          title: Text('Option 1'),
          value: 1,
          groupValue: 1,
          onChanged: (value) {},
        ),
        SizedBox(height: 20),

        // Switch
        SwitchListTile(
          title: Text('Enable notifications'),
          value: true,
          onChanged: (value) {},
        ),
        SizedBox(height: 20),

        // Slider
        Slider(
          value: 0.5,
          onChanged: (value) {},
        ),
        SizedBox(height: 20),

        // Progress Indicator
        CircularProgressIndicator(),
        SizedBox(height: 10),
        LinearProgressIndicator(),
      ],
    ),
  ),
);

} } ```_

Materialkomponenten

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

class MaterialComponents extends StatelessWidget { @override Widget build(BuildContext context) { return Scaffold( appBar: AppBar(title: Text('Material Components')), drawer: Drawer( child: ListView( children: [ DrawerHeader(child: Text('Drawer Header')), ListTile(title: Text('Item 1')), ListTile(title: Text('Item 2')), ], ), ), body: Center( child: Column( mainAxisAlignment: MainAxisAlignment.center, children: [ // Card Card( child: Padding( padding: EdgeInsets.all(16.0), child: Text('This is a Card'), ), ), SizedBox(height: 20),

        // Chip
        Chip(
          avatar: CircleAvatar(child: Text('A')),
          label: Text('Chip'),
        ),
        SizedBox(height: 20),

        // DataTable
        DataTable(
          columns: [
            DataColumn(label: Text('ID')),
            DataColumn(label: Text('Name')),
          ],
          rows: [
            DataRow(cells: [DataCell(Text('1')), DataCell(Text('John'))]),
            DataRow(cells: [DataCell(Text('2')), DataCell(Text('Jane'))]),
          ],
        ),
        SizedBox(height: 20),

        // SnackBar
        RaisedButton(
          onPressed: () {
            Scaffold.of(context).showSnackBar(
              SnackBar(content: Text('This is a SnackBar')),
            );
          },
          child: Text('Show SnackBar'),
        ),
      ],
    ),
  ),
  floatingActionButton: FloatingActionButton(
    onPressed: () {},
    child: Icon(Icons.add),
  ),
  bottomNavigationBar: BottomNavigationBar(
    items: [
      BottomNavigationBarItem(icon: Icon(Icons.home), label: 'Home'),
      BottomNavigationBarItem(icon: Icon(Icons.search), label: 'Search'),
      BottomNavigationBarItem(icon: Icon(Icons.person), label: 'Profile'),
    ],
  ),
);

} } ```_

Layouts

Single-Child Layout Widgets

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

class SingleChildLayouts extends StatelessWidget { @override Widget build(BuildContext context) { return Scaffold( appBar: AppBar(title: Text('Single-Child Layouts')), body: Column( children: [ // Container Container( color: Colors.blue, padding: EdgeInsets.all(16.0), margin: EdgeInsets.all(16.0), child: Text('Container'), ),

      // Center
      Center(
        child: Text('Center'),
      ),

      // Padding
      Padding(
        padding: EdgeInsets.all(16.0),
        child: Text('Padding'),
      ),

      // Align
      Align(
        alignment: Alignment.bottomRight,
        child: Text('Align'),
      ),

      // SizedBox
      SizedBox(
        width: 200,
        height: 100,
        child: Card(child: Center(child: Text('SizedBox'))),
      ),

      // AspectRatio
      AspectRatio(
        aspectRatio: 16 / 9,
        child: Container(color: Colors.green),
      ),

      // ConstrainedBox
      ConstrainedBox(
        constraints: BoxConstraints(maxWidth: 200, maxHeight: 100),
        child: Container(color: Colors.red),
      ),
    ],
  ),
);

} } ```_

Multi-Child Layout Widgets

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

class MultiChildLayouts extends StatelessWidget { @override Widget build(BuildContext context) { return Scaffold( appBar: AppBar(title: Text('Multi-Child Layouts')), body: Column( children: [ // Row Row( mainAxisAlignment: MainAxisAlignment.spaceEvenly, children: [Text('Row 1'), Text('Row 2'), Text('Row 3')], ),

      // Column
      Column(
        crossAxisAlignment: CrossAxisAlignment.start,
        children: [Text('Column 1'), Text('Column 2'), Text('Column 3')],
      ),

      // Stack
      Stack(
        children: [
          Container(width: 100, height: 100, color: Colors.red),
          Container(width: 80, height: 80, color: Colors.green),
          Container(width: 60, height: 60, color: Colors.blue),
        ],
      ),

      // ListView
      Expanded(
        child: ListView(
          children: [
            ListTile(title: Text('Item 1')),
            ListTile(title: Text('Item 2')),
            ListTile(title: Text('Item 3')),
          ],
        ),
      ),

      // GridView
      Expanded(
        child: GridView.count(
          crossAxisCount: 2,
          children: List.generate(4, (index) => Center(child: Text('Item $index'))),
        ),
      ),
    ],
  ),
);

} } ```_

Navigation

Navigator 1.0 (Imperativ)

```dart // Navigate to a new screen Navigator.push( context, MaterialPageRoute(builder: (context) => DetailsScreen()), );

// Navigate back Navigator.pop(context);

// Navigate with data Navigator.push( context, MaterialPageRoute( builder: (context) => DetailsScreen(item: item), ), );

// Receive data from a screen final result = await Navigator.push( context, MaterialPageRoute(builder: (context) => SelectionScreen()), );

// Send data back Navigator.pop(context, 'Yes'); ```_

Navigator 2.0 (Erklärung)

```dart // pubspec.yaml dependencies: flutter: sdk: flutter go_router: ^3.0.0

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

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

class MyApp extends StatelessWidget { @override Widget build(BuildContext context) { return MaterialApp.router( routeInformationParser: _router.routeInformationParser, routerDelegate: _router.routerDelegate, ); }

final _router = GoRouter( routes: [ GoRoute( path: '/', builder: (context, state) => HomeScreen(), ), GoRoute( path: '/details/:id', builder: (context, state) => DetailsScreen(id: state.params['id']!), ), ], ); }

// Navigate with go_router context.go('/details/123'); context.push('/details/456'); ```_

Staatliche Verwaltung

Anbieter

```dart // pubspec.yaml dependencies: provider: ^6.0.0

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

void main() { runApp( ChangeNotifierProvider( create: (context) => Counter(), child: MyApp(), ), ); }

class Counter with ChangeNotifier { int _count = 0; int get count => _count;

void increment() { _count++; notifyListeners(); } }

// Usage in a widget class CounterScreen extends StatelessWidget { @override Widget build(BuildContext context) { return Scaffold( appBar: AppBar(title: Text('Provider Example')), body: Center( child: Text('Count: ${context.watch().count}'), ), floatingActionButton: FloatingActionButton( onPressed: () => context.read().increment(), child: Icon(Icons.add), ), ); } } ```_

BLoC (Business Logic Component)

```dart // pubspec.yaml dependencies: flutter_bloc: ^8.0.0

// counter_event.dart abstract class CounterEvent {} class Increment extends CounterEvent {}

// counter_bloc.dart import 'package:bloc/bloc.dart'; import 'counter_event.dart';

class CounterBloc extends Bloc { CounterBloc() : super(0) { on((event, emit) => emit(state + 1)); } }

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

void main() { runApp( BlocProvider( create: (context) => CounterBloc(), child: MyApp(), ), ); }

// Usage in a widget class CounterScreen extends StatelessWidget { @override Widget build(BuildContext context) { return Scaffold( appBar: AppBar(title: Text('BLoC Example')), body: Center( child: BlocBuilder( builder: (context, count) => Text('Count: $count'), ), ), floatingActionButton: FloatingActionButton( onPressed: () => context.read().add(Increment()), child: Icon(Icons.add), ), ); } } ```_

Riverpod

```dart // pubspec.yaml dependencies: flutter_riverpod: ^1.0.0

// main.dart import 'package:flutter/material.dart'; import 'package:flutter_riverpod/flutter_riverpod.dart';

final counterProvider = StateProvider((ref) => 0);

void main() { runApp(ProviderScope(child: MyApp())); }

// Usage in a widget class CounterScreen extends ConsumerWidget { @override Widget build(BuildContext context, WidgetRef ref) { final count = ref.watch(counterProvider);

return Scaffold(
  appBar: AppBar(title: Text('Riverpod Example')),
  body: Center(
    child: Text('Count: $count'),
  ),
  floatingActionButton: FloatingActionButton(
    onPressed: () => ref.read(counterProvider.state).state++,
    child: Icon(Icons.add),
  ),
);

} } ```_

Vernetzung

http-Paket

```dart // pubspec.yaml dependencies: http: ^0.13.0

// services/api_service.dart import 'package:http/http.dart' as http; import 'dart:convert';

class ApiService { Future> fetchData() async { final response = await http.get(Uri.parse('https://jsonplaceholder.typicode.com/posts/1')); if (response.statusCode == 200) { return json.decode(response.body); } else { throw Exception('Failed to load data'); } } } ```_

Dio Paket

```dart // pubspec.yaml dependencies: dio: ^4.0.0

// services/api_service.dart import 'package:dio/dio.dart';

class ApiService { final dio = Dio();

Future> fetchData() async { try { final response = await dio.get('https://jsonplaceholder.typicode.com/posts/1'); return response.data; } catch (e) { throw Exception('Failed to load data'); } } } ```_

Persistenz

Shared_Präferenzen

```dart // pubspec.yaml dependencies: shared_preferences: ^2.0.0

// utils/storage.dart import 'package:shared_preferences/shared_preferences.dart';

class Storage { Future saveUsername(String username) async { final prefs = await SharedPreferences.getInstance(); await prefs.setString('username', username); }

Future getUsername() async { final prefs = await SharedPreferences.getInstance(); return prefs.getString('username'); } } ```_

Sqflite

```dart // pubspec.yaml dependencies: sqflite: ^2.0.0 path: ^1.8.0

// services/database_service.dart import 'package:sqflite/sqflite.dart'; import 'package:path/path.dart';

class DatabaseService { late Database _database;

Future initDatabase() async { _database = await openDatabase( join(await getDatabasesPath(), 'my_database.db'), onCreate: (db, version) { return db.execute( 'CREATE TABLE users(id INTEGER PRIMARY KEY, name TEXT, age INTEGER)', ); }, version: 1, ); }

Future insertUser(Map user) async { await _database.insert('users', user, conflictAlgorithm: ConflictAlgorithm.replace); }

Future>> getUsers() async { return await database.query('users'); } } ```

Animationen

Implizite Animationen

```dart class ImplicitAnimation extends StatefulWidget { @override _ImplicitAnimationState createState() => _ImplicitAnimationState(); }

class _ImplicitAnimationState extends State { bool _isBig = false;

@override Widget build(BuildContext context) { return GestureDetector( onTap: () => setState(() => isBig = !_isBig), child: AnimatedContainer( duration: Duration(seconds: 1), width: _isBig ? 200 : 100, height: _isBig ? 200 : 100, color: _isBig ? Colors.blue : Colors.red, ), ); } } ```

Explicit Animationen

```dart class ExplicitAnimation extends StatefulWidget { @override _ExplicitAnimationState createState() => _ExplicitAnimationState(); }

class _ExplicitAnimationState extends State with SingleTickerProviderStateMixin { late AnimationController _controller; late Animation _animation;

@override void initState() { super.initState(); _controller = AnimationController(vsync: this, duration: Duration(seconds: 2)); _animation = Tween(begin: 0, end: 300).animate(_controller) ..addListener(() => setState(() {})); _controller.forward(); }

@override void dispose() { _controller.dispose(); super.dispose(); }

@override Widget build(BuildContext context) { return Container( width: animation.value, height: _animation.value, color: Colors.green, ); } } ```

Integration von Plattformen

MethodChannel

```dart // Dart side import 'package:flutter/services.dart';

const platform = MethodChannel('com.example.myapp/channel');

Future getBatteryLevel() async { try { final int result = await platform.invokeMethod('getBatteryLevel'); return 'Battery level at $result % .'; } on PlatformException catch (e) { return "Failed to get battery level: '${e.message}'."; } }

// Android side (MainActivity.java) import io.flutter.embedding.android.FlutterActivity; import io.flutter.plugin.common.MethodChannel;

public class MainActivity extends FlutterActivity { private static final String CHANNEL = "com.example.myapp/channel";

@Override public void configureFlutterEngine(@NonNull FlutterEngine flutterEngine) { super.configureFlutterEngine(flutterEngine); new MethodChannel(flutterEngine.getDartExecutor().getBinaryMessenger(), CHANNEL) .setMethodCallHandler( (call, result) -> { if (call.method.equals("getBatteryLevel")) { // ... get battery level result.success(batteryLevel); } } ); } } ```_

Prüfung

Einheitsprüfung

```dart // test/counter_test.dart import 'package:test/test.dart'; import 'package:my_app/counter.dart';

void main() { test('Counter value should be incremented', () { final counter = Counter(); counter.increment(); expect(counter.value, 1); }); } ```_

Widget Testing

```dart // test/widget_test.dart import 'package:flutter/material.dart'; import 'package:flutter_test/flutter_test.dart'; import 'package:my_app/main.dart';

void main() { testWidgets('Counter increments smoke test', (WidgetTester tester) async { await tester.pumpWidget(MyApp());

expect(find.text('0'), findsOneWidget);
expect(find.text('1'), findsNothing);

await tester.tap(find.byIcon(Icons.add));
await tester.pump();

expect(find.text('0'), findsNothing);
expect(find.text('1'), findsOneWidget);

}); } ```_

Integrationstests

```dart // test_driver/app_test.dart import 'package:flutter_driver/flutter_driver.dart'; import 'package:test/test.dart';

void main() { group('Counter App', () { FlutterDriver driver;

setUpAll(() async {
  driver = await FlutterDriver.connect();
});

tearDownAll(() async {
  if (driver != null) {
    driver.close();
  }
});

test('increments the counter', () async {
  final counterTextFinder = find.byValueKey('counter');
  final buttonFinder = find.byValueKey('increment');

  expect(await driver.getText(counterTextFinder), '0');

  await driver.tap(buttonFinder);

  expect(await driver.getText(counterTextFinder), '1');
});

}); } ```_

Debugging

DevTools

```bash

Open DevTools from the terminal

flutter pub global activate devtools flutter pub global run devtools

Or from VS Code / Android Studio

```_

Protokoll

```dart import 'dart:developer' as developer;

void myFunction() { developer.log('This is a log message', name: 'my.app.category'); } ```_

Bereitstellung

Android

```bash

Build an APK

flutter build apk

Build an App Bundle

flutter build appbundle ```_

iOS

```bash

Build an IPA

flutter build ipa ```_

Web

```bash

Build for web

flutter build web ```_

Best Practices

• *Follow Effektive Dart Leitlinien: Schreiben Sie sauber, pflegeleicht Dart-Code.
• *Organisieren Sie Ihre Projektstruktur: Halten Sie Ihren Code organisiert und einfach zu navigieren.
• ** Verwenden Sie eine staatliche Managementlösung*: Wählen Sie eine State Management Lösung, die der Komplexität Ihrer App entspricht.
• *Writtests: Schreibeinheit, Widget und Integrationstests, um sicherzustellen, dass Ihre App richtig funktioniert.
• Optimieren Sie die Leistung: Verwenden Sie DevTools, um Leistungsengpässe zu identifizieren und zu beheben.
• *Handle-Fehler anmutig: Verwenden Sie Try-Catch Blöcke und Fehler Widgets, um Fehler zu handhaben.

Fehlerbehebung

Gemeinsame Themen

• *Platformspezifische Probleme: Überprüfen Sie Ihren Plattformaufbau (Android Studio, Xcode).
• ** Abhängigkeitskonflikte*: Führen Sie flutter pub deps aus, um nach Abhängigkeitskonflikten zu suchen.
• Baufehler: Führen Sie flutter clean und dann flutter pub get_ aus, um Ihre Build-Dateien zu reinigen.

--

Zusammenfassung

Flutter ist ein leistungsstarkes und flexibles UI-Toolkit zum Aufbau hochwertiger, plattformübergreifender Anwendungen. Die wichtigsten Funktionen sind:

• Fast Development: Heißes Nachladen ermöglicht es Ihnen, Änderungen sofort zu sehen.
• *Expressive UI: Erstellen Sie schöne und benutzerdefinierte UIs mit einem reichen Satz von Widgets.
• Native Performance: Flutter-Apps werden auf nativen Code kompiliert und bieten hervorragende Leistungen.
• *Single Codebase: Einmal schreiben, auf Handy, Web und Desktop laufen.
• *Growing Community: Eine große und aktive Gemeinschaft bietet Unterstützung und ein reiches Ökosystem an Paketen.

Flutter ist eine ausgezeichnete Wahl für Entwickler, die schöne, leistungsstarke Anwendungen für mehrere Plattformen mit einer einzigen Codebasis erstellen möchten.

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