Advanced MobX Techniques: Mastering Multiple Stores in Flutter

7.4.2 Working with Multiple Stores

In the world of state management, especially when using MobX in Flutter, the concept of multiple stores can significantly enhance the modularity and maintainability of your application. This section delves into the intricacies of working with multiple stores, providing you with the knowledge to effectively manage state across various domains of your app.

Concept of Multiple Stores

When and Why to Use Multiple Stores

In a complex application, it’s crucial to separate concerns to maintain a clean and manageable codebase. By using multiple stores, you can:

• Enhance Modularity: Each store can focus on a specific domain or feature of your application, such as user management, task management, or settings.
• Improve Maintainability: Smaller, focused stores are easier to maintain, test, and debug.
• Facilitate Team Collaboration: Different team members can work on separate stores without interfering with each other’s code.
• Optimize Performance: By isolating state changes to specific stores, you can reduce unnecessary updates and improve performance.

Benefits of Focused Stores

Focused stores allow you to encapsulate logic and state related to a particular feature or domain. This separation helps in:

• Reducing Complexity: Each store handles a specific part of the application’s state, making the logic simpler and more understandable.
• Reusability: Stores can be reused across different parts of the application or even in different projects.
• Scalability: As your application grows, you can add more stores without affecting existing ones.

Communicating Between Stores

While keeping stores independent is ideal, there are scenarios where stores need to interact. For example, a UserStore might need to clear tasks in a TaskStore upon user logout.

Injecting Dependencies

One way to facilitate communication between stores is through dependency injection. This allows one store to access and manipulate the state of another store safely.

Here’s an example of how you can achieve this:

class UserStore = _UserStore with _$UserStore;

abstract class _UserStore with Store {
  final TaskStore taskStore;

  _UserStore(this.taskStore);

  @action
  void logout() {
    // Perform logout operations
    taskStore.clearTasks();
  }
}

In this example, UserStore has a dependency on TaskStore, allowing it to clear tasks when a user logs out.

Avoiding Circular Dependencies

Circular dependencies occur when two or more stores depend on each other, creating a loop that can lead to runtime errors and difficult-to-debug issues. To avoid this:

• Use Interfaces: Define interfaces for stores to interact with each other, reducing direct dependencies.
• Service Locator Pattern: Use a service locator to manage dependencies and resolve them at runtime.
• Constructor Injection: Prefer constructor injection to set dependencies explicitly, making the dependencies clear and manageable.

Injection Strategies

Constructor Injection

Constructor injection is a straightforward method where dependencies are passed to the store through its constructor. This method is explicit and makes it easy to see what dependencies a store requires.

Service Locator Pattern

A service locator is a design pattern that provides a centralized registry for managing dependencies. It allows you to resolve dependencies at runtime, offering flexibility and decoupling.

Using the Provider Package

The Provider package in Flutter is a popular choice for dependency injection. It allows you to provide stores to the widget tree, making them accessible to any widget that needs them.

void main() {
  final taskStore = TaskStore();
  final userStore = UserStore(taskStore);

  runApp(
    MultiProvider(
      providers: [
        Provider<TaskStore>.value(value: taskStore),
        Provider<UserStore>.value(value: userStore),
      ],
      child: MyApp(),
    ),
  );
}

Best Practices

• Keep Stores Independent: Minimize dependencies between stores to reduce coupling and increase flexibility.
• Document Interactions: Clearly document how stores interact with each other to improve maintainability and facilitate onboarding for new developers.
• Test Store Interactions: Write tests to ensure that interactions between stores work as expected and do not introduce bugs.

Code Examples

Let’s consider an application that manages users and tasks. We’ll split the logic into two stores: UserStore and TaskStore.

UserStore

class UserStore = _UserStore with _$UserStore;

abstract class _UserStore with Store {
  final TaskStore taskStore;

  _UserStore(this.taskStore);

  @observable
  String username;

  @action
  void login(String name) {
    username = name;
    // Additional login logic
  }

  @action
  void logout() {
    username = null;
    taskStore.clearTasks();
  }
}

TaskStore

class TaskStore = _TaskStore with _$TaskStore;

abstract class _TaskStore with Store {
  @observable
  ObservableList<String> tasks = ObservableList<String>();

  @action
  void addTask(String task) {
    tasks.add(task);
  }

  @action
  void clearTasks() {
    tasks.clear();
  }
}

Mermaid.js Diagrams

To better understand the relationships and data flow between multiple stores, let’s visualize it using a Mermaid.js diagram.

    graph TD;
	    UserStore -->|uses| TaskStore;
	    TaskStore -->|provides| TaskData;
	    UserStore -->|modifies| UserData;
	    TaskData -->|updates| UI;
	    UserData -->|updates| UI;

This diagram illustrates how UserStore and TaskStore interact and update the UI.

Key Takeaways

• Scalability: Multiple stores allow you to scale your application’s state management effectively.
• Modularity: By separating concerns, you can keep your codebase clean and maintainable.
• Flexibility: With dependency injection, stores can interact without tight coupling, providing flexibility in how you structure your application.

By mastering the use of multiple stores in MobX, you can build robust, scalable, and maintainable Flutter applications. Remember to keep stores focused, document interactions, and use dependency injection wisely to avoid pitfalls.

Quiz Time!