flutter-managing-state

Flutter state management depends on scope: use StatefulWidget with setState for ephemeral state local to one widget, and use the provider package with ChangeNotifier for app state shared across multiple widgets. The MVVM pattern keeps views lean and logic in ViewModels.

Use setState only for ephemeral state contained within a single widget, such as the current tab or animation progress. Use Provider with ChangeNotifier when state is shared across multiple parts of the app or persists between user sessions, like login info or cart contents.

Create a Repository as the single source of truth, then a ViewModel extending ChangeNotifier that exposes UI state and calls notifyListeners on changes. Inject it with ChangeNotifierProvider, consume it with Consumer for rebuilds, and use context.read inside event handlers.

The most common cause is a missing notifyListeners() call after mutating state in the ChangeNotifier. Also verify the widget is wrapped in a Consumer or listens via Provider.of with listen set to true, and that the provider is placed above the consuming widget in the tree.

setState only rebuilds the widget that owns the State object, so it cannot share data across distant widgets without prop drilling. For shared state like user sessions or carts, it leads to tangled code; use InheritedWidget-based solutions like provider instead.