Saving the State of ListView.builder in Flutter Drawer: A Comprehensive Guide

Are you tired of losing the state of your ListView.builder every time you close and reopen your Flutter drawer? Do you want to preserve the scrolled position and selection of your list even when the drawer is closed? You’re not alone! In this article, we’ll dive into the world of state management in Flutter and explore ways to save the state of your ListView.builder in the drawer.

The Problem: Losing State on Drawer Close

When you use a ListView.builder in a Flutter drawer, you might notice that the state of the list is lost whenever you close and reopen the drawer. This can be frustrating, especially if your list has a large number of items and the user has scrolled down to a specific position. You might have tried using AutomaticKeepAliveClientMixin, but unfortunately, it doesn’t work in this scenario.

So, why does this happen? The reason lies in the way Flutter handles the drawer’s widget tree. When you close the drawer, the entire widget tree is disposed, and when you reopen it, a new instance of the widget tree is created. This means that any state held by the widgets in the drawer is lost, including the scrolled position and selection of your ListView.builder.

Solution 1: Using Provider and ChangeNotifier

One way to preserve the state of your ListView.builder is to use the Provider package in combination with ChangeNotifier. This approach involves creating a separate class that holds the state of your list and notifies the widgets to rebuild when the state changes.

// Create a separate class to hold the state of your list
class ListState with ChangeNotifier {
  int _scrollPosition = 0;

  int get scrollPosition => _scrollPosition;

  void updateScrollPosition(int position) {
    _scrollPosition = position;
    notifyListeners();
  }
}

// Wrap your MaterialApp with a ChangeNotifierProvider
ChangeNotifierProvider(
  create: (_) => ListState(),
  child: MaterialApp(
    // Your app's widget tree
  ),
)

// In your drawer, create a Consumer to listen to changes in the ListState
Consumer(
  builder: (context, listState, child) {
    return ListView.builder(
      itemCount: 100,
      itemBuilder: (context, index) {
        return ListTile(
          title: Text('Item $index'),
        );
      },
      // Save the scrolled position when the list is scrolled
      onScroll: (scrollPosition) {
        listState.updateScrollPosition(scrollPosition);
      },
    );
  },
)

In this example, we create a ListState class that holds the scrolled position of the list and notifies the widgets to rebuild when the state changes. We then wrap our MaterialApp with a ChangeNotifierProvider to provide the ListState instance to our widgets. Finally, we create a Consumer in our drawer to listen to changes in the ListState and update the scrolled position accordingly.

Solution 2: Using Riverpod and StateNotifier

Riverpod is a provider library that provides a simpler way to manage state in Flutter. We can use Riverpod’s StateNotifier to preserve the state of our ListView.builder.

// Create a separate class to hold the state of your list
class ListState with StateNotifier {
  int _scrollPosition = 0;

  int get scrollPosition => _scrollPosition;

  void updateScrollPosition(int position) {
    _scrollPosition = position;
    state = AsyncData(_scrollPosition);
  }
}

// Create a Riverpod provider for your list state
final listStateProvider = StateNotifierProvider((ref) => ListState());

// In your drawer, use the Riverpod provider to access the list state
Consumer-widget(
  builder: (context, ref, child) {
    final listState = ref.watch(listStateProvider);

    return ListView.builder(
      itemCount: 100,
      itemBuilder: (context, index) {
        return ListTile(
          title: Text('Item $index'),
        );
      },
      // Save the scrolled position when the list is scrolled
      onScroll: (scrollPosition) {
        listState.updateScrollPosition(scrollPosition);
      },
    );
  },
)

In this example, we create a ListState class that holds the scrolled position of the list and uses Riverpod’s StateNotifier to notify the widgets to rebuild when the state changes. We then create a Riverpod provider for the list state and use it in our drawer to access the list state and update the scrolled position accordingly.

Solution 3: Using a Global Key

A more simple approach is to use a global key to save the state of your ListView.builder. This method involves creating a GlobalKey for your ListView.builder and using it to save the scrolled position.

// Create a GlobalKey for your ListView.builder
final GlobalKey _listKey = GlobalKey();

// In your drawer, use the GlobalKey to save the scrolled position
ListView.builder(
  key: _listKey,
  itemCount: 100,
  itemBuilder: (context, index) {
    return ListTile(
      title: Text('Item $index'),
    );
  },
  onScroll: (scrollPosition) {
    // Save the scrolled position when the list is scrolled
    _listKey.currentState.scrollPosition = scrollPosition;
  },
)

In this example, we create a GlobalKey for our ListView.builder and use it to save the scrolled position when the list is scrolled. When the drawer is reopened, we can use the GlobalKey to restore the scrolled position.

Best Practices and Considerations

When preserving the state of your ListView.builder, there are a few best practices and considerations to keep in mind:

• Use a separate class to hold the state: This approach makes it easier to manage the state of your list and ensures that the state is preserved even when the drawer is closed.
• Use a provider or riverpod to manage state: Providers and Riverpod make it easy to manage state in Flutter and provide a simple way to notify widgets to rebuild when the state changes.
• Save the state when the list is scrolled: Use the onScroll callback to save the scrolled position when the list is scrolled.
• Restore the state when the drawer is reopened: Use the saved state to restore the scrolled position when the drawer is reopened.

Conclusion

In this article, we explored three solutions to preserve the state of a ListView.builder in a Flutter drawer. We covered using Provider and ChangeNotifier, Riverpod and StateNotifier, and a global key to save the state of the list. By following these solutions and best practices, you can ensure that the state of your ListView.builder is preserved even when the drawer is closed and reopened.

I hope this article has been helpful in solving your problem. Remember to always follow best practices and consider the complexity of your app when choosing a solution. Happy coding!

Solution	Provider	Riverpod
1	Provider and ChangeNotifier	No
2	No	Riverpod and StateNotifier
3	No	No

Note: The table above compares the three solutions discussed in this article.

Related Articles

• 10 Best Practices for Managing State in Flutter
• A Beginner’s Guide to Provider in Flutter
• Riverpod vs Provider: Which One to Choose?

I hope you found this article helpful. If you have any questions or need further assistance, please don’t hesitate to ask.

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