ChangeNotifier class Null safety

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).

Improve rebuilds performance using AnimatedBuilder

Despite the name, AnimatedBuilder is not limited to Animations. Any subtype of Listenable (such as ChangeNotifier and ValueNotifier) can be used with an AnimatedBuilder to rebuild only certain parts of a widget when the Listenable notifies its listeners. This technique is a performance improvement that allows rebuilding only specific widgets leaving others untouched.

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

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

Constructors

ChangeNotifier()

Properties

hashCode → int: The hash code for this object.
read-onlyinherited
hasListeners → bool: Whether any listeners are currently registered.
protected">@protectedread-only
runtimeType → Type: A representation of the runtime type of the object.
read-onlyinherited

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).
mustCallSuper">@mustCallSuper
noSuchMethod(Invocation invocation) → dynamic: Invoked when a non-existent method or property is accessed.
inherited
notifyListeners() → void: Call all the registered listeners.
protected">@protectedvisibleForTesting">@visibleForTesting
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.