Mastering GoRouter: How to Keep the State of Just Some Routes

Are you tired of struggling with state management in your Flutter app when using GoRouter? Do you wish there was a way to preserve the state of specific routes, while allowing others to be recreated from scratch? Well, you’re in luck! In this comprehensive guide, we’ll dive into the world of GoRouter and explore the secrets of maintaining state for select routes.

Understanding GoRouter and State Management

Before we dive into the nitty-gritty, let’s take a step back and review the basics. GoRouter is a popular routing package for Flutter that provides a simple and intuitive way to navigate between screens. However, when it comes to state management, GoRouter can be a bit…tricky.

By default, GoRouter recreates the entire widget tree whenever the app navigates to a new route. This means that any state stored in widgets will be lost when navigating away and recreated when returning. While this behavior is desirable in many cases, it can be problematic when dealing with complex, stateful widgets.

The Problem: Losing State on Route Changes

Imagine you have a route that displays a list of items, and the user can filter the list by selecting specific categories. When the user navigates away from this route and returns later, the filter selections are lost, and the list is recreated from scratch. Not ideal, right?

That’s where the concept of “stateful routes” comes in. A stateful route is one that preserves its state even when the app navigates away and returns later. But how can we achieve this magic with GoRouter?

Introducing Stateful GoRouter: The Solution

The secret to keeping state for specific routes lies in GoRouter’s `Scope` and `Delegate` mechanisms. By utilizing these features, we can create stateful routes that preserve their state even when navigating away and returning later.

Step 1: Create a StatefulScope

To create a stateful scope, we need to define a `Scope` that will manage the state of our route. This scope will be responsible for storing and retrieving the state of our route.

// Define a scope for our stateful route
class MyStatefulScope extends Scope {
  @override
  Widget builder(Widget child) {
    // Create a stateful widget that will store the state
    return StatefulMyRouteWidget();
  }
}

Step 2: Define a StatefulRoute Widget

Next, we need to define a stateful widget that will store the state of our route. This widget will be responsible for storing and retrieving the state from the scope.

// Define a stateful widget that will store the state
class StatefulMyRouteWidget extends StatefulWidget {
  @override
  _StatefulMyRouteWidgetState createState() => _StatefulMyRouteWidgetState();
}

class _StatefulMyRouteWidgetState extends State<StatefulMyRouteWidget> {
  // Store the state in a variable
  List<String> _selectedCategories = [];

  // Initialize the state from the scope
  @override
  void didChangeDependencies() {
    super.didChangeDependencies();
    // Get the scope from the context
    final scope = context.findScope<MyStatefulScope>();
    // Initialize the state from the scope
    _selectedCategories = scope.getState();
  }

  // Update the state in the scope
  void _updateState() {
    // Get the scope from the context
    final scope = context.findScope<MyStatefulScope>();
    // Update the state in the scope
    scope.setState(_selectedCategories);
  }

  // Build the widget
  @override
  Widget build(BuildContext context) {
    // Build the widget using the stored state
    return ListView.builder(
      itemCount: _selectedCategories.length,
      itemBuilder: (context, index) {
        return ListTile(
          title: Text(_selectedCategories[index]),
        );
      },
    );
  }
}

Step 3: Configure GoRouter to Use the StatefulScope

Finally, we need to configure GoRouter to use our stateful scope when navigating to our route.

// Define a GoRouter configuration
GoRouter _router = GoRouter(
  // Define the routes
  routes: [
    GoRoute(
      // Define the route path
      path: '/my-route',
      // Define the stateful scope
      scope: MyStatefulScope(),
      // Define the route builder
      builder: (context) => StatefulMyRouteWidget(),
    ),
  ],
);

And that’s it! With these three steps, we’ve successfully created a stateful route that preserves its state even when navigating away and returning later.

Tips and Variations

Now that we’ve covered the basics, let’s explore some additional tips and variations to take your stateful route game to the next level.

Using a GlobalScope for Shared State

In some cases, you may want to share state between multiple routes. To achieve this, you can use a `GlobalScope` that stores the shared state.

// Define a global scope for shared state
class MyAppGlobalScope extends GlobalScope {
  // Store the shared state
  List<String> _sharedState = [];
}

// Use the global scope in your routes
GoRouter _router = GoRouter(
  routes: [
    GoRoute(
      path: '/route1',
      scope: MyAppGlobalScope(),
      builder: (context) => Route1Widget(),
    ),
    GoRoute(
      path: '/route2',
      scope: MyAppGlobalScope(),
      builder: (context) => Route2Widget(),
    ),
  ],
);

Using a Custom Delegate for Advanced State Management

In more complex scenarios, you may need to implement custom state management logic. To achieve this, you can create a custom `Delegate` that manages the state of your route.

// Define a custom delegate for advanced state management
class MyCustomDelegate extends Delegate {
  @override
  void didPush(Route route, Route previousRoute) {
    // Implement custom state management logic here
  }

  @override
  void didPop(Route route, Route previousRoute) {
    // Implement custom state management logic here
  }
}

// Use the custom delegate in your GoRouter configuration
GoRouter _router = GoRouter(
  delegate: MyCustomDelegate(),
  routes: [
    // Define your routes here
  ],
);

Conclusion

In this comprehensive guide, we’ve explored the world of GoRouter and learned how to keep the state of just some routes. By using `Scope` and `Delegate` mechanisms, we can create stateful routes that preserve their state even when navigating away and returning later.

Remember, state management is a critical aspect of building robust and user-friendly Flutter apps. By mastering GoRouter’s state management features, you can take your app to the next level and provide a seamless user experience.

Keyword	Explanation
GoRouter	A popular routing package for Flutter
Scope	A mechanism for managing state in GoRouter
Delegate	A mechanism for customizing state management in GoRouter
Stateful Route	A route that preserves its state even when navigating away and returning later

By following the instructions in this guide, you’ll be well on your way to mastering GoRouter and creating stateful routes that delight your users. Happy coding!

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