Flutter State Management

State management is one of the most important concepts in developing applications with Flutter, as it is an important aspect of designing robust and user-friendly applications. State management is responsible for managing and updating the application’s state over time according to user input, and is the engine behind most of the UX user experience. At its core, state management is about organizing and managing the changes in state within an application. This can range from user-generated changes like form fields being filled out, to changes in application data, to changes in system states like device orientation. By utilizing state management techniques, developers can ensure that the application has a consistent, reliable behavior over time.

Guide to Flutter State Management

1. Identify Your State Management Needs

The first step in implementing a Flutter state management system is to identify the different types of state that need to be managed in the application. This includes user input, system state, application state, and component data. All of these need to be identified in order to plan out an effective state management structure.

2. Choose an Appropriate State Management Library

Once the different types of state have been identified, the next step is to choose an appropriate state management library for your application. Flutter has several options for state management, including the Bloc (Business Logic Component) pattern, the Provider pattern, and Redux. Each of these libraries has their own set of strengths and weaknesses, so it’s important to choose one that is best suited for your application’s needs.

3. Design the State Management Structure

Once the library has been chosen, the next step is to design the state management structure. This includes creating the services and models that will manage the application’s state, and deciding how best to connect them together. It is important to ensure that the structure is clean, efficient, and well-structured in order to ensure that the application’s state can be effectively managed.

4. Implement the State Management System

Once the state management structure has been designed, it’s time to begin implementation. This includes writing the code to connect the services and models together, as well as creating the views and widgets to display the application’s state. This is perhaps the most challenging part of the process, and it is important to ensure that the code is well-structured and efficient.

State management libraries

There are several ways to manage the state of a Flutter application, and the most common approaches include using the Provider pattern, using the BLoC architecture, and using Redux.

The Provider

The Provider pattern is a simple approach to state management in Flutter. It is based on the Provider package, which provides a mechanism for sharing data across multiple widgets in Flutter applications. The Provider pattern involves wrapping a widget with a Provider, which can then be accessed by any widget that needs access to the data.

For example, if you needed to keep track of the user’s current location in the application, you could wrap the widget with a LocationProvider, which would allow any widget to use the location data.

The BLoC

The BLoC (Business Logic Component) architecture is a more advanced approach to state management in Flutter. It is based on the concept of separating the business logic from the UI, allowing for a more maintainable and testable application.

The BLoC architecture involves creating BLoCs, which are components that contain the business logic, and Widgets, which are components that contain the UI.

The BLoCs are responsible for handling the data and the Widgets are responsible for displaying the data. A good example of using the BLoC architecture is when creating a form in the application.

The BLoC can be used to manage the form data and the Widgets can be used to display the data.

Redux

Redux is a state management library that has been growing in popularity since its introduction in 2015. It is based on the concept of unidirectional data flow, which simplifies state management by ensuring that data flows through the application in a predictable and consistent way.

The Redux architecture consists of four components: the store, the reducers, the actions, and the views. The store is responsible for holding the global state, the reducers are responsible for modifying the state, the actions are responsible for dispatching the changes, and the views are responsible for displaying the state. A good example of using Redux is when creating an authentication flow for the application.

The store can be used to manage the user’s authentication state and the reducers, actions, and views can be used to manage the authentication flow.

Conclusion

State management is an essential part of any Flutter application, and it is important to ensure that it is properly implemented in order to create robust and user-friendly applications. By properly identifying the different types of state that need to be managed, choosing the appropriate state management library, designing the state management structure, and finally implementing the system, developers can ensure that their applications are well-structured, efficient, and maintainable over time.

Full Example

In this example, we’ll create a Flutter application that uses the Provider package to manage state. The example will be simple enough to understand and highlight some of the major features of Provider.

First, we’ll create a basic file structure. It should include:

– main.dart
– lib directory
– models directory
– services directory

Inside the lib directory, we’ll create the main page of the application: MainPage.dart. This page will contain 2 widgets – a counter widget and a button. The button will increment the counter value stored in the state.

Next, we’ll create a file in the models directory called Counter.dart. This will contain the Counter model, which will hold the current count.

Moving on, we’ll create a new file in the services directory called CounterService.dart. This file will contain the logic for incrementing the counter. It will also contain a method to reset the counter.

Now that we have the basic structure set up, let’s start writing the code.

First, we’ll add the dependencies to pubspec.yaml. We’ll need the Provider package and flutter_hooks.

dependencies:
  flutter:
    sdk: flutter
  provider: ^4.3.2
  flutter_hooks: ^0.7.2

Next, we’ll import the necessary packages in our main.dart file.

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

We’ll also create an instance of the CounterService, which will be used to manage the counter state.

// Main.dart 
final counterService = CounterService();

Now, let’s write the Counter model and CounterService classes. The Counter model will contain the current count and a method to increment the count. The CounterService will contain the logic for incrementing the count and resetting the Counter model.

// Counter.dart 
class Counter { 
  int count; 

  Counter({this.count = 0}); 

  void increment(){ 
    count++; 
  }
}

// CounterService.dart 
class CounterService { 
  Counter counter; 

  CounterService(){ 
    counter = Counter(count: 0); 
  } 

  void incrementCounter(){ 
    counter.increment(); 
  } 

  void resetCounter(){ 
    counter = Counter(count: 0); 
  }
}

Now, let’s create the MainPage widget. We’ll use the Provider package to manage the Counter state and the Hooks package to access it in our widget.

// MainPage.dart 

class MainPage extends StatelessWidget{ 
  @override 
  Widget build(BuildContext context){ 
    return Provider( 
      create: (_) => counterService, 
      child: Scaffold( 
        appBar: AppBar( 
          title: Text('Flutter State Management Example'), 
        ), 
        body: Center( 
          child: Column( 
            mainAxisAlignment: MainAxisAlignment.center, 
            children: <Widget>[ 
              Text( 
                'You have pushed the button this many times:', 
              ), 
              // Get the counter value using the Hooks package. 
              CounterWidget(), 
              RaisedButton( 
                onPressed: () { 
                  // Increment the counter value using the Provider package. 
                  Provider.of<CounterService>(context, listen: false).incrementCounter(); 
                }, 
                child: Text('Increment'), 
              ) 
            ], 
          ), 
        ), 
      ), 
    ); 
  }
}

// CounterWidget.dart 

class CounterWidget extends HookWidget { 
  @override 
  Widget build(BuildContext context) { 
    // Get the CounterService instance using the Hooks package 
    final counterService = useProvider<CounterService>(); 

    return Text( 
      '${counterService.counter.count}', 
      style: Theme.of(context).textTheme.headline4, 
    ); 
  }
}

Finally, we’ll call the MainPage widget in our main.dart file.

// Main.dart 
void main(){ 
  runApp(MyApp()); 
} 

class MyApp extends StatelessWidget { 
  @override 
  Widget build(BuildContext context) { 
    return MaterialApp( 
      title: 'Flutter Demo', 
      theme: ThemeData( 
        primarySwatch: Colors.blue, 
      ), 
      home: MainPage(), 
    ); 
  }
}

This is a complete example of managing state in a Flutter application using Provider and Hooks. The Provider package allows us to access the CounterService instance and update the counter value. The Hooks package allows us to easily access the CounterService instance and get the current count.