Flutter State Management

Are you tired of managing state in your Flutter applications? Do you find yourself constantly passing data between widgets and struggling to keep track of changes? Fear not, because Flutter has a variety of state management solutions to make your life easier.

In this article, we'll explore the different approaches to state management in Flutter and help you choose the best one for your project.

What is State Management?

Before we dive into the different state management solutions, let's first define what we mean by "state". In Flutter, state refers to any data that can change during the lifetime of a widget. This can include user input, network requests, or even changes to the device's orientation.

State management is the process of managing this data and ensuring that it is updated and displayed correctly in your application. This can involve passing data between widgets, storing data in a central location, or using a reactive programming model.

The Flutter Stateful Widget

The most basic form of state management in Flutter is the Stateful Widget. This widget has an associated State object that can hold data and update the widget when it changes.

To use a Stateful Widget, simply create a new class that extends StatefulWidget and implement the createState() method. This method returns a new instance of the associated State object.

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 Scaffold(
      appBar: AppBar(
        title: Text('My Widget'),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            Text(
              'You have pushed the button this many times:',
            ),
            Text(
              '$_counter',
              style: Theme.of(context).textTheme.headline4,
            ),
          ],
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: _incrementCounter,
        tooltip: 'Increment',
        child: Icon(Icons.add),
      ),
    );
  }
}

In this example, we create a simple counter that increments each time the user presses a button. The _incrementCounter() method updates the _counter variable and calls setState() to notify the framework that the widget needs to be rebuilt.

InheritedWidget

While Stateful Widgets are great for managing local state within a widget, they can become cumbersome when passing data between widgets. InheritedWidget provides a solution to this problem by allowing data to be passed down the widget tree without the need for explicit passing.

InheritedWidget is a widget that can hold data and pass it down to its descendants. To use InheritedWidget, simply create a new class that extends InheritedWidget and implement the updateShouldNotify() method. This method is called whenever the data changes and determines whether the widget's descendants should be rebuilt.

class MyData extends InheritedWidget {
  final int data;

  MyData({Key key, @required this.data, @required Widget child})
      : super(key: key, child: child);

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

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

In this example, we create a simple InheritedWidget that holds an integer value. The updateShouldNotify() method compares the new data to the old data and returns true if they are different. The static of() method is used to retrieve the data from the widget tree.

To use the MyData widget, simply wrap it around any widgets that need access to the data.

class MyWidget extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MyData(
      data: 42,
      child: Scaffold(
        appBar: AppBar(
          title: Text('My Widget'),
        ),
        body: Center(
          child: Column(
            mainAxisAlignment: MainAxisAlignment.center,
            children: <Widget>[
              Text(
                'The answer to life, the universe, and everything:',
              ),
              Text(
                '${MyData.of(context).data}',
                style: Theme.of(context).textTheme.headline4,
              ),
            ],
          ),
        ),
      ),
    );
  }
}

In this example, we wrap the MyData widget around a Scaffold and display the data in a Text widget. The MyData.of() method is used to retrieve the data from the widget tree.

Provider

While InheritedWidget provides a simple solution for passing data down the widget tree, it can become cumbersome when dealing with complex data structures or large amounts of data. Provider provides a more robust solution by allowing data to be stored in a central location and accessed by any widget in the tree.

Provider is a package that provides a simple way to manage state in your Flutter applications. It uses the InheritedWidget pattern to provide a central location for storing data and allows widgets to access this data using a Provider widget.

To use Provider, simply wrap your widget tree with a MultiProvider widget and provide a list of providers.

void main() {
  runApp(
    MultiProvider(
      providers: [
        ChangeNotifierProvider(create: (_) => Counter()),
      ],
      child: MyApp(),
    ),
  );
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'My App',
      home: MyWidget(),
    );
  }
}

In this example, we create a MultiProvider widget and provide a single provider for a Counter object. The Counter object is a simple class that extends ChangeNotifier and holds a single integer value.

class Counter extends ChangeNotifier {
  int _count = 0;

  int get count => _count;

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

In this example, we create a simple Counter class that holds a count value and provides a method for incrementing it. The notifyListeners() method is called whenever the count value changes to notify any listeners.

To use the Counter object in a widget, simply use the Provider.of() method to retrieve it from the widget tree.

class MyWidget extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    final counter = Provider.of<Counter>(context);

    return Scaffold(
      appBar: AppBar(
        title: Text('My Widget'),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            Text(
              'You have pushed the button this many times:',
            ),
            Text(
              '${counter.count}',
              style: Theme.of(context).textTheme.headline4,
            ),
          ],
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: () => counter.increment(),
        tooltip: 'Increment',
        child: Icon(Icons.add),
      ),
    );
  }
}

In this example, we use the Provider.of() method to retrieve the Counter object and display the count value in a Text widget. The onPressed() method of the FloatingActionButton calls the increment() method of the Counter object to update the count value.

BLoC

BLoC (Business Logic Component) is a design pattern that separates the business logic of an application from the user interface. It provides a way to manage state in a predictable and testable way by using streams to communicate between the business logic and the user interface.

To use BLoC in your Flutter application, you'll need to use the flutter_bloc package. This package provides a set of classes and widgets for implementing the BLoC pattern.

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'My App',
      home: BlocProvider(
        create: (context) => CounterBloc(),
        child: MyWidget(),
      ),
    );
  }
}

In this example, we create a CounterBloc object and provide it to the MyWidget widget using a BlocProvider widget. The CounterBloc object is a simple class that extends the Bloc class and holds a single integer value.

class CounterBloc extends Bloc<CounterEvent, int> {
  CounterBloc() : super(0);

  @override
  Stream<int> mapEventToState(CounterEvent event) async* {
    if (event is IncrementEvent) {
      yield state + 1;
    }
  }
}

In this example, we create a simple CounterBloc class that extends the Bloc class and holds a count value. The mapEventToState() method is called whenever an event is added to the bloc and returns a stream of state changes.

To use the CounterBloc object in a widget, simply use the BlocBuilder widget to listen for state changes and update the user interface.

class MyWidget extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    final counterBloc = BlocProvider.of<CounterBloc>(context);

    return Scaffold(
      appBar: AppBar(
        title: Text('My Widget'),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            Text(
              'You have pushed the button this many times:',
            ),
            BlocBuilder<CounterBloc, int>(
              builder: (context, count) {
                return Text(
                  '$count',
                  style: Theme.of(context).textTheme.headline4,
                );
              },
            ),
          ],
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: () => counterBloc.add(IncrementEvent()),
        tooltip: 'Increment',
        child: Icon(Icons.add),
      ),
    );
  }
}

In this example, we use the BlocBuilder widget to listen for state changes and update the count value in a Text widget. The onPressed() method of the FloatingActionButton adds an IncrementEvent to the CounterBloc to update the count value.

Conclusion

State management is an important aspect of any Flutter application. Whether you're managing local state within a widget or passing data between widgets, Flutter has a variety of solutions to make your life easier.

In this article, we've explored the different approaches to state management in Flutter, including Stateful Widgets, InheritedWidget, Provider, and BLoC. Each approach has its own strengths and weaknesses, so it's important to choose the best one for your project.

So what are you waiting for? Start managing your state like a pro with Flutter!

Editor Recommended Sites