Flutter Widgets

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Introduction

Flutter is a mobile application development framework that allows developers to create high-performance, visually appealing, and cross-platform mobile applications. Flutter is built using the Dart programming language, which is a modern, object-oriented programming language that is easy to learn and use.

Flutter is an open-source framework that is backed by Google, and it has a large and active community of developers who contribute to its development and maintenance. Flutter is gaining popularity among developers due to its ease of use, flexibility, and performance.

This cheatsheet is designed to provide a comprehensive overview of the concepts, topics, and categories related to Flutter and Dart. It is intended for beginners who are just getting started with Flutter and Dart, and it covers everything from basic concepts to advanced topics.

Flutter Widgets

Flutter widgets are the building blocks of a Flutter application. Widgets are the visual elements that make up the user interface of a Flutter application. Widgets can be simple, such as a button or a text field, or they can be complex, such as a list view or a custom widget.

There are two types of widgets in Flutter: stateless widgets and stateful widgets. Stateless widgets are widgets that do not change over time, while stateful widgets are widgets that can change over time.

Stateless Widgets

Stateless widgets are widgets that do not change over time. They are immutable and do not have any internal state. Stateless widgets are used to display static content, such as text, images, or icons.

To create a stateless widget, you need to extend the StatelessWidget class and override the build method. The build method returns a widget that describes the user interface of the widget.

Example:

class MyWidget extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Text('Hello, World!');
  }
}

Stateful Widgets

Stateful widgets are widgets that can change over time. They have internal state that can be updated based on user interactions or other events. Stateful widgets are used to display dynamic content, such as user input or data from an API.

To create a stateful widget, you need to extend the StatefulWidget class and override the createState method. The createState method returns a state object that manages the internal state of the widget.

Example:

class MyWidget extends StatefulWidget {
  @override
  _MyWidgetState createState() => _MyWidgetState();
}

class _MyWidgetState extends State<MyWidget> {
  int _counter = 0;

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

  @override
  Widget build(BuildContext context) {
    return Column(
      children: <Widget>[
        Text('You have clicked the button $_counter times.'),
        RaisedButton(
          onPressed: _incrementCounter,
          child: Text('Click me!'),
        ),
      ],
    );
  }
}

Layout Widgets

Layout widgets are widgets that are used to arrange other widgets in a specific layout. Layout widgets are used to create the user interface of a Flutter application.

There are several layout widgets available in Flutter, including:

• Container: A widget that can contain other widgets and provides padding, margin, and decoration.
• Row: A widget that arranges its children in a horizontal line.
• Column: A widget that arranges its children in a vertical line.
• Stack: A widget that arranges its children in layers.
• Expanded: A widget that expands to fill the available space in a row or column.

Example:

class MyWidget extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Container(
      padding: EdgeInsets.all(16.0),
      margin: EdgeInsets.all(16.0),
      decoration: BoxDecoration(
        color: Colors.grey[200],
        borderRadius: BorderRadius.circular(8.0),
      ),
      child: Column(
        children: <Widget>[
          Text('Hello, World!'),
          Row(
            children: <Widget>[
              Expanded(
                child: RaisedButton(
                  onPressed: () {},
                  child: Text('Button 1'),
                ),
              ),
              Expanded(
                child: RaisedButton(
                  onPressed: () {},
                  child: Text('Button 2'),
                ),
              ),
            ],
          ),
        ],
      ),
    );
  }
}

Navigation

Navigation is the process of moving between different screens or pages in a Flutter application. Navigation is an important part of any mobile application, and Flutter provides several ways to implement navigation in an application.

There are two types of navigation in Flutter: push navigation and modal navigation. Push navigation is used to move between screens in a linear fashion, while modal navigation is used to display a screen on top of another screen.

Push Navigation

Push navigation is used to move between screens in a linear fashion. In push navigation, a new screen is pushed onto the navigation stack, and the user can navigate back to the previous screen by popping the current screen off the stack.

To implement push navigation in Flutter, you need to use the Navigator widget and the MaterialPageRoute class. The Navigator widget manages the navigation stack, while the MaterialPageRoute class creates a new screen and pushes it onto the stack.

Example:

class MyHomePage extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Home'),
      ),
      body: Center(
        child: RaisedButton(
          onPressed: () {
            Navigator.push(
              context,
              MaterialPageRoute(
                builder: (context) => MySecondPage(),
              ),
            );
          },
          child: Text('Go to second page'),
        ),
      ),
    );
  }
}

class MySecondPage extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Second Page'),
      ),
      body: Center(
        child: RaisedButton(
          onPressed: () {
            Navigator.pop(context);
          },
          child: Text('Go back'),
        ),
      ),
    );
  }
}

Modal Navigation

Modal navigation is used to display a screen on top of another screen. In modal navigation, the current screen is not removed from the navigation stack, and the user can dismiss the modal screen to return to the previous screen.

To implement modal navigation in Flutter, you need to use the Navigator widget and the MaterialPageRoute class. The Navigator widget manages the navigation stack, while the MaterialPageRoute class creates a new screen and displays it as a modal screen.

Example:

class MyHomePage extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Home'),
      ),
      body: Center(
        child: RaisedButton(
          onPressed: () {
            Navigator.push(
              context,
              MaterialPageRoute(
                fullscreenDialog: true,
                builder: (context) => MyModalPage(),
              ),
            );
          },
          child: Text('Open modal'),
        ),
      ),
    );
  }
}

class MyModalPage extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Modal Page'),
      ),
      body: Center(
        child: RaisedButton(
          onPressed: () {
            Navigator.pop(context);
          },
          child: Text('Close modal'),
        ),
      ),
    );
  }
}

State Management

State management is the process of managing the internal state of a Flutter application. State management is an important part of any mobile application, and Flutter provides several ways to implement state management in an application.

There are several state management techniques available in Flutter, including:

• InheritedWidget: A widget that allows data to be passed down the widget tree.
• Provider: A package that provides a simple way to manage state using InheritedWidget.
• BLoC: A pattern that separates the business logic from the user interface.
• Redux: A pattern that manages the state of an application using a single store.

InheritedWidget

InheritedWidget is a widget that allows data to be passed down the widget tree. InheritedWidget is used to share data between widgets without having to pass the data through each widget.

To use InheritedWidget in Flutter, you need to create a new class that extends the InheritedWidget class. The InheritedWidget class provides a method called of that can be used to retrieve the data from the widget tree.

Example:

class MyData extends InheritedWidget {
  final int count;

  MyData({this.count, Widget child}) : super(child: child);

  static MyData of(BuildContext context) {
    return context.dependOnInheritedWidgetOfExactType<MyData>();
  }

  @override
  bool updateShouldNotify(MyData oldWidget) {
    return count != oldWidget.count;
  }
}

class MyWidget extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MyData(
      count: 42,
      child: Text(MyData.of(context).count.toString()),
    );
  }
}

Provider

Provider is a package that provides a simple way to manage state using InheritedWidget. Provider is a popular state management technique in Flutter, and it is used by many developers to manage the state of their applications.

To use Provider in Flutter, you need to add the provider package to your project and create a new class that extends the ChangeNotifier class. The ChangeNotifier class provides a method called notifyListeners that can be used to notify the listeners when the state changes.

Example:

class MyModel extends ChangeNotifier {
  int _count = 0;

  int get count => _count;

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

class MyWidget extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Consumer<MyModel>(
      builder: (context, model, child) {
        return Text(model.count.toString());
      },
    );
  }
}

BLoC

BLoC is a pattern that separates the business logic from the user interface. BLoC is a popular state management technique in Flutter, and it is used by many developers to manage the state of their applications.

To use BLoC in Flutter, you need to create a new class that extends the Bloc class. The Bloc class provides a method called mapEventToState that can be used to map the events to the new state.

Example:

enum MyEvent { increment }

class MyBloc extends Bloc<MyEvent, int> {
  @override
  int get initialState => 0;

  @override
  Stream<int> mapEventToState(MyEvent event) async* {
    switch (event) {
      case MyEvent.increment:
        yield state + 1;
        break;
    }
  }
}

class MyWidget extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return BlocBuilder<MyBloc, int>(
      builder: (context, count) {
        return Text(count.toString());
      },
    );
  }
}

Redux

Redux is a pattern that manages the state of an application using a single store. Redux is a popular state management technique in Flutter, and it is used by many developers to manage the state of their applications.

To use Redux in Flutter, you need to add the redux package to your project and create a new class that extends the Reducer class. The Reducer class provides a method called reduce that can be used to reduce the state based on the action.

Example:

enum MyAction { increment }

class MyState {
  final int count;

  MyState({this.count});

  MyState copyWith({int count}) {
    return MyState(count: count ?? this.count);
  }
}

class MyReducer extends Reducer<MyState, MyAction> {
  @override
  MyState reduce(MyState state, MyAction action) {
    switch (action) {
      case MyAction.increment:
        return state.copyWith(count: state.count + 1);
        break;
      default:
        return state;
    }
  }
}

class MyWidget extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return StoreConnector<MyState, int>(
      converter: (store) => store.state.count,
      builder: (context, count) {
        return Text(count.toString());
      },
    );
  }
}

Conclusion

Flutter is a powerful mobile application development framework that allows developers to create high-performance, visually appealing, and cross-platform mobile applications. Flutter is built using the Dart programming language, which is a modern, object-oriented programming language that is easy to learn and use.

This cheatsheet has provided a comprehensive overview of the concepts, topics, and categories related to Flutter and Dart. It has covered everything from basic concepts to advanced topics, including Flutter widgets, navigation, state management, and more.

Whether you are a beginner or an experienced developer, this cheatsheet will provide you with the information you need to get started with Flutter and Dart. So, go ahead and start building your next mobile application using Flutter and Dart!

Common Terms, Definitions and Jargon

1. Flutter: A mobile application development framework created by Google that allows developers to build high-performance, cross-platform apps for iOS and Android.
2. Dart: A programming language developed by Google that is used to build web and mobile applications.
3. Widget: A graphical user interface (GUI) component that can be used to create the user interface of a Flutter app.
4. Stateful Widget: A widget that can change its state during the lifetime of the app.
5. Stateless Widget: A widget that does not change its state during the lifetime of the app.
6. Material Design: A design language developed by Google that is used to create visually appealing and consistent user interfaces across different platforms.
7. Cupertino Design: A design language developed by Apple that is used to create visually appealing and consistent user interfaces across different platforms.
8. Scaffold Widget: A widget that provides a basic structure for a Flutter app, including a navigation drawer, app bar, and body.
9. AppBar Widget: A widget that provides a navigation bar at the top of the screen.
10. BottomNavigationBar Widget: A widget that provides a navigation bar at the bottom of the screen.
11. FloatingActionButton Widget: A widget that provides a floating action button that can be used to trigger an action.
12. ListView Widget: A widget that displays a scrollable list of items.
13. GridView Widget: A widget that displays a grid of items.
14. Card Widget: A widget that displays a card with a title, subtitle, and content.
15. TextField Widget: A widget that allows users to enter text.
16. RaisedButton Widget: A widget that displays a button that can be pressed.
17. FlatButton Widget: A widget that displays a button that can be pressed.
18. IconButton Widget: A widget that displays an icon that can be pressed.
19. AlertDialog Widget: A widget that displays a dialog box with a message and buttons.
20. Navigator Widget: A widget that manages the navigation between different screens in a Flutter app.

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