How GetIt Works

GetIt is a service locator for Dart and Flutter projects. It's essentially a lightweight dependency injection container that allows you to register instances of classes and retrieve them anywhere in your app.

Key Concepts:

1. Registration: You register instances or factory functions with GetIt.
2. Resolution: You retrieve those instances when needed.
3. Scoping: You can control the lifetime of registered instances.

Registration Types:

• Singleton: A single instance is created and reused throughout the app.
• LazySingleton: Similar to singleton, but the instance is created only when first requested.
• Factory: A new instance is created each time you request it.

Data Persistence and GetIt

GetIt itself does not handle data persistence between app sessions. It's an in-memory service locator, so when the app is closed, all registered instances are lost. When the app is reopened, GetIt starts fresh and you need to register your instances again.

What GetIt Does NOT Do:

• It doesn't save data to disk
• It doesn't automatically restore state when the app restarts
• It doesn't persist between app sessions

What GetIt IS Used For:

• Managing dependencies during a single app session
• Providing a clean way to access services throughout your app
• Avoiding passing instances through constructors (dependency injection)

How to Handle Data Persistence

For data that needs to persist between app sessions, you need to use other mechanisms alongside GetIt:

1. Local Storage: Use packages like shared_preferences, sqflite, or flutter_secure_storage to save data to disk.

2. Load on Startup: When your app starts, load the data from storage and then register it with GetIt.

Example of Persistence with GetIt:

// On app startup
void setupDependencies() async {
  // 1. Load data from persistent storage
  final savedCategories = await loadCategoriesFromDatabase();
  
  // 2. Create your service with the loaded data
  final categoryService = CategoryService(initialCategories: savedCategories);
  
  // 3. Register with GetIt
  GetIt.instance.registerSingleton<CategoryService>(categoryService);
}

// When data changes
void updateCategories(List<CategoryModel> newCategories) async {
  // 1. Update the service (already registered in GetIt)
  final service = GetIt.instance<CategoryService>();
  service.updateCategories(newCategories);
  
  // 2. Save to persistent storage
  await saveCategoriesInDatabase(newCategories);
}

In Your Current Implementation

In your app, you're already handling persistence correctly:

1. You're using SQLite (via sqflite) to store data in a local database.
2. You're using flutter_secure_storage for sensitive data.
3. GetIt is just being used to provide access to services and blocs.

The data flow is:

• Data is stored in the database
• Services/blocs access the database
• GetIt provides access to those services/blocs

When the app restarts:

1. GetIt registers fresh instances of services/blocs
2. Those services load data from the database
3. The UI displays the loaded data

Conclusion

GetIt itself doesn't handle persistence between app sessions - it's just an in-memory service locator. For data that needs to persist, you need to use other storage mechanisms (which you're already doing with SQLite and secure storage).

The pattern you're using is correct:

1. Store data in persistent storage
2. Use GetIt to provide access to services that interact with that storage
3. Load data from storage when needed

This approach gives you both the convenience of dependency injection during the app session and proper data persistence between sessions.