8.13. State management in Flutter: Sharing state across screens

State management is one of the most important aspects of app development, and Flutter is no different. State management in Flutter refers to the way data is stored and manipulated within the app. In simple terms, state is information that can be read synchronously when the widget is built and can change during the lifetime of the widget.

One of the most common ways to manage state in Flutter is through the use of the StatefulWidget. However, when the state needs to be shared across multiple screens, or when the state is complex, the StatefulWidget might not be the best solution. For such scenarios, Flutter offers several other options for managing state, including InheritedWidget, Provider, Redux, Bloc, and others.

To better understand state management in Flutter, let's consider a scenario where we have multiple screens and need to share state between them. For example, let's assume we are building a shopping cart application, where the user can add items to the cart from several different screens. Here, the shopping cart state needs to be shared across multiple screens.

One of the ways to share state between screens is to use the InheritedWidget. The InheritedWidget is a widget that defines a data dependency for child widgets. It stores the data that will be shared between child widgets. When the data changes, the InheritedWidget ensures that all dependent widgets are rebuilt.

To use the InheritedWidget, we first need to create a class that extends the InheritedWidget. In the constructor of this class, we pass the data we want to share. We then use the updateShouldNotify method to determine when to notify dependent widgets about data changes.

While the InheritedWidget can be a viable solution for sharing state across screens, it does have some limitations. For example, it's not ideal for scenarios where the state is complex or where the state needs to be shared across many widgets. Also, the InheritedWidget doesn't provide an easy way to listen for changes in state.

To overcome these limitations, we can use Provider. Provider is a package that simplifies state management in Flutter. It combines the ideas of InheritedWidget and ScopedModel to provide a powerful and flexible state management solution.

To use the Provider, we first need to define a class that contains the state we want to share. We then use the ChangeNotifierProvider to create an instance of this class and make it available to descendant widgets. Widgets that depend on state can then use the Consumer to listen for changes in state.

Another option for state management in Flutter is Redux. Redux is a predictable state management pattern that helps you write applications that behave consistently and are easy to test. In Redux, state is stored in a single object, called a store, which can be accessed from anywhere in the application. When the state changes, Redux ensures that all widgets that depend on the state are rebuilt.

Finally, Bloc is another popular option for state management in Flutter. Bloc is a library that implements the Bloc (Business Logic Component) design pattern to separate business logic from the user interface. In Bloc, state is represented by event flows and states, which are manipulated by blocks.

In summary, state management is a crucial part of app development in Flutter. Depending on your application's needs, you can choose from several options for managing state, including StatefulWidget, InheritedWidget, Provider, Redux, and Bloc. Each of these options has its own advantages and disadvantages, so choosing the best option depends on your application's specific needs.

Next page of the Free Ebook:

115State Management in Flutter: State Scopes

3 minutes