When would you use App state or Ephemeral state over another?

When deciding between using App state or Ephemeral state in Flutter, you should consider the scope and lifetime of the state, as well as the nature of the data you need to manage. Both approaches have their use cases, and choosing the right one depends on the specific requirements of your application.

App state (Global State):

  1. Scope and Lifetime: App state represents data that needs to be accessed and shared across multiple widgets or screens within your application. It has a global scope and persists throughout the entire lifecycle of the app.
  2. Data Sharing: App state is suitable for data that needs to be shared and synchronized across different parts of the app, allowing widgets at different levels of the widget tree to access and update the same data.
  3. State Management Solutions: To manage app state effectively, you can use state management solutions like Provider, Bloc, Riverpod, or other third-party packages that offer a centralized way to manage and update state across the app.
  4. Examples of App State: User authentication status, theme settings, shopping cart data, user preferences, etc.

Ephemeral state (Local State):

  1. Scope and Lifetime: Ephemeral state represents data that is only relevant and needed within a specific widget or widget subtree. It is short-lived and exists only as long as the widget tree remains active.
  2. Data Isolation: Ephemeral state is suitable for data that does not need to be shared with other widgets or screens. It remains isolated within the widget that owns it, and any changes to the state are local to that widget or its descendants.
  3. Local State Management: To manage ephemeral state, you can use Flutter’s built-in setState() method or other local state management techniques like InheritedWidget, ValueNotifier, or Getx, depending on the complexity and size of the widget tree.
  4. Examples of Ephemeral State: Form input values, UI visibility toggles, loading indicators, local animation state, etc.

When to use App state:

  • When you need to share and synchronize data across multiple parts of the app or between different screens.
  • When the data needs to persist throughout the entire app lifecycle and should not be affected by individual widget rebuilds.
  • When the state management complexity exceeds what can be handled efficiently with local state management.

When to use Ephemeral state:

  • When the data is only relevant and used within a specific widget or a small subtree of widgets.
  • When the state is short-lived and doesn’t need to be accessible outside of its owning widget tree.
  • When the state management is relatively simple and can be efficiently handled using local state management techniques.

In many cases, a combination of both App state and Ephemeral state is used in a Flutter app to effectively manage the state at different levels of the widget tree. Careful consideration of the scope and requirements of the data will help you determine which approach is best suited for each situation.

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