ChangeNotifier class mixin

A class that can be extended or mixed in that provides a change notification API using VoidCallback for notifications.

It is O(1) for adding listeners and O(N) for removing listeners and dispatching notifications (where N is the number of listeners).

Using ChangeNotifier subclasses for data models

A data structure can extend or mix in ChangeNotifier to implement the Listenable interface and thus become usable with widgets that listen for changes to Listenables, such as ListenableBuilder.

The following example implements a simple counter that utilizes a ListenableBuilder to limit rebuilds to only the Text widget containing the count. The current count is stored in a ChangeNotifier subclass, which rebuilds the ListenableBuilder's contents when its value is changed.

To create a local project with this code sample, run:
flutter create --sample=foundation.ChangeNotifier.1 mysample

In this case, the ChangeNotifier subclass encapsulates a list, and notifies the clients any time an item is added to the list. This example only supports adding items; as an exercise, consider adding buttons to remove items from the list as well.

To create a local project with this code sample, run:
flutter create --sample=foundation.ChangeNotifier.2 mysample

Constructors

ChangeNotifier()

Properties

hashCode → int: The hash code for this object.
no setterinherited
hasListeners → bool: Whether any listeners are currently registered.
no setter
runtimeType → Type: A representation of the runtime type of the object.
no setterinherited

Methods

addListener(VoidCallback listener) → void: Register a closure to be called when the object changes.
override
dispose() → void: Discards any resources used by the object. After this is called, the object is not in a usable state and should be discarded (calls to addListener will throw after the object is disposed).
noSuchMethod(Invocation invocation) → dynamic: Invoked when a nonexistent method or property is accessed.
inherited
notifyListeners() → void: Call all the registered listeners.
removeListener(VoidCallback listener) → void: Remove a previously registered closure from the list of closures that are notified when the object changes.
override
toString() → String: A string representation of this object.
inherited

Operators

operator ==(Object other) → bool: The equality operator.
inherited

Static Methods

debugAssertNotDisposed(ChangeNotifier notifier) → bool: Used by subclasses to assert that the ChangeNotifier has not yet been disposed.
maybeDispatchObjectCreation(ChangeNotifier object) → void: Dispatches event of the object creation to FlutterMemoryAllocations.instance.