ChangeNotifierProvider

ChangeNotifierProvider is a widget from the Flutter provider package that supplies a ChangeNotifier to its descendant widgets. It creates and holds a ChangeNotifier instance and makes it available to the widget subtree, enabling UI components to react to changes in the model.

In typical usage, a developer creates a model class that extends ChangeNotifier and wraps part of the widget tree with ChangeNotifierProvider(create: (context) => MyModel()). The MyModel class should call notifyListeners() whenever its state changes, which signals listening widgets to rebuild.

Widgets can subscribe to the provided notifier in several ways. The simplest is to use context.watch<MyModel>(), which causes the calling widget to rebuild when notifyListeners is called. Alternatively, a Consumer<MyModel> can be used to rebuild only a portion of the widget tree in response to changes. If a widget only needs to read the model once without listening for changes, context.read<MyModel>() can be used.

Disposal is managed by the provider: when the ChangeNotifierProvider is removed from the widget tree, the provided ChangeNotifier is disposed automatically if it was created by the provider. If an existing ChangeNotifier instance is being reused, ChangeNotifierProvider.value can be used to supply that instance to the subtree without creating a new one.

This pattern is widely used for managing simple, reactive state in Flutter apps and pairs well with other provider utilities, such as MultiProvider, for composing multiple sources of state.