AnimatedBuilder class Null safety

A general-purpose widget for building animations.

AnimatedBuilder is useful for more complex widgets that wish to include an animation as part of a larger build function. To use AnimatedBuilder, simply construct the widget and pass it a builder function.

For simple cases without additional state, consider using AnimatedWidget.

Performance optimizations

If your builder function contains a subtree that does not depend on the animation, it's more efficient to build that subtree once instead of rebuilding it on every animation tick.

If you pass the pre-built subtree as the child parameter, the AnimatedBuilder will pass it back to your builder function so that you can incorporate it into your build.

Using this pre-built child is entirely optional, but can improve performance significantly in some cases and is therefore a good practice.

This code defines a widget that spins a green square continually. It is built with an AnimatedBuilder and makes use of the child feature to avoid having to rebuild the Container each time.

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

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

AnimatedBuilder({Key? key, required Listenable animation, required TransitionBuilder builder, Widget? child}): Creates an animated builder.
const

Properties

builder → TransitionBuilder: Called every time the animation changes value.
final
child → Widget?: The child widget to pass to the builder.
final
hashCode → int: The hash code for this object.
nonVirtual">@nonVirtualread-onlyinherited
key → Key?: Controls how one widget replaces another widget in the tree.
finalinherited
listenable → Listenable: The Listenable to which this widget is listening.
finalinherited
runtimeType → Type: A representation of the runtime type of the object.
read-onlyinherited

Methods

build(BuildContext context) → Widget: Override this method to build widgets that depend on the state of the listenable (e.g., the current value of the animation).
override
createElement() → StatefulElement: Creates a StatefulElement to manage this widget's location in the tree.
inherited
createState() → State<AnimatedWidget>: Subclasses typically do not override this method.
inherited
debugDescribeChildren() → List<DiagnosticsNode>: Returns a list of DiagnosticsNode objects describing this node's children.
protected">@protectedinherited
debugFillProperties(DiagnosticPropertiesBuilder properties) → void: Add additional properties associated with the node.
inherited
noSuchMethod(Invocation invocation) → dynamic: Invoked when a non-existent method or property is accessed.
inherited
toDiagnosticsNode({String? name, DiagnosticsTreeStyle? style}) → DiagnosticsNode: Returns a debug representation of the object that is used by debugging tools and by DiagnosticsNode.toStringDeep.
inherited
toString({DiagnosticLevel minLevel = DiagnosticLevel.info}) → String: A string representation of this object.
inherited
toStringDeep({String prefixLineOne = '', String? prefixOtherLines, DiagnosticLevel minLevel = DiagnosticLevel.debug}) → String: Returns a string representation of this node and its descendants.
inherited
toStringShallow({String joiner = ', ', DiagnosticLevel minLevel = DiagnosticLevel.debug}) → String: Returns a one-line detailed description of the object.
inherited
toStringShort() → String: A short, textual description of this widget.
inherited

Operators

operator ==(Object other) → bool: The equality operator.
nonVirtual">@nonVirtualinherited

Flutter
widgets
AnimatedBuilder class