Flutter Hydrated Bloc always replaced with the initial state and not persisting

ONLINECAST

3 min read

·

05-10-2024

4

0

Share

Flutter Hydrated Bloc: Why Your State Isn't Persisting (And How To Fix It)

Have you ever encountered a situation where your Flutter Hydrated Bloc seems to be ignoring your persistent state? It's frustrating to see the app consistently revert to its initial state instead of loading the saved data. This article will help you diagnose and resolve this common issue, ensuring your state persists across app sessions.

The Scenario: Lost State in the Mist

Imagine you have a simple shopping cart app built with Flutter and Hydrated Bloc. You add items to your cart, exit the app, and upon reopening, expect to see those items still present. However, you're greeted by an empty cart, as if you had just started fresh. This is the classic symptom of a Hydrated Bloc not properly persisting its state.

Here's an example of how your code might look:

import 'package:hydrated_bloc/hydrated_bloc.dart';

class CartBloc extends HydratedBloc<CartState, CartEvent> {
  CartBloc() : super(CartState());

  @override
  Stream<CartState> mapEventToState(CartEvent event) {
    // ... logic to update the cart state
  }

  @override
  CartState? fromJson(Map<String, dynamic> json) {
    return CartState.fromJson(json);
  }

  @override
  Map<String, dynamic>? toJson(CartState state) {
    return state.toJson();
  }
}

class CartState {
  // ... cart state properties
}

Common Culprits: Unveiling the Root Cause

The most likely reasons for your Hydrated Bloc not persisting state are:

1. Storage Issues: The storage mechanism (either LocalStorage or HiveStorage) might be malfunctioning. Double-check your setup, permissions, and storage paths.
2. Missing Dependencies: The Hydrated Bloc package might not be correctly integrated into your main app. Make sure you've initialized HydratedStorage in your main function.
3. Incorrect State Serialization: The fromJson and toJson methods in your state class might not be handling serialization properly. Ensure they correctly map the state's properties to and from JSON.
4. Caching Issues: If your application uses caching, there might be conflicts between cached data and the state stored by Hydrated Bloc. Consider clearing cache to isolate the issue.

Troubleshooting and Debugging

1. Verify Storage Functionality: Use a tool like flutter doctor or adb shell to inspect the storage location where Hydrated Bloc is saving state. Check for the presence of the state file and its contents.
2. Examine State Serialization: Print out the JSON representation of your state before saving and after loading to ensure the serialization process is accurate.
3. Utilize Logging: Include debug statements in your fromJson and toJson methods to monitor the flow of data and pinpoint potential errors.
4. Isolate the Problem: Create a minimal, reproducible example to rule out any external influences on the state persistence behavior.

Fixing the Issue: A Comprehensive Solution

Here's a breakdown of how to fix common state persistence issues:

1. Ensure Storage Configuration:

   void main() async {
     WidgetsFlutterBinding.ensureInitialized();
     await HydratedStorage.build(); // Initialize Hydrated Storage
     runApp(MyApp());
   }
   

2. Implement Correct Serialization:

   // CartState.dart
   class CartState {
     List<CartItem> items;
   
     CartState({required this.items});
   
     factory CartState.fromJson(Map<String, dynamic> json) {
       return CartState(
         items: List<CartItem>.from(
           json['items'].map((item) => CartItem.fromJson(item)),
         ),
       );
     }
   
     Map<String, dynamic> toJson() {
       return {
         'items': items.map((item) => item.toJson()).toList(),
       };
     }
   }
   

3. Handle State Updates Correctly:

   // CartBloc.dart
   class CartBloc extends HydratedBloc<CartState, CartEvent> {
     CartBloc() : super(CartState(items: [])); // Initial state
   
     @override
     Stream<CartState> mapEventToState(CartEvent event) {
       if (event is AddItemEvent) {
         return emit(state.copyWith(
           items: [...state.items, event.item],
         ));
       } else if (event is RemoveItemEvent) {
         // ...
       }
       // ... other event handling logic
     }
   
     // ... fromJson and toJson methods
   }
   

By addressing these points, you'll dramatically increase your chances of achieving reliable state persistence in your Flutter Hydrated Bloc.

Conclusion: A Persistent Solution

Understanding the causes of persistent state issues in Flutter Hydrated Bloc is crucial for building seamless and user-friendly applications. By following the troubleshooting and debugging steps outlined in this article, and implementing robust serialization and state management practices, you can ensure your application's state consistently persists across sessions, providing a smooth and engaging user experience.