AnimatedFractionallySizedBox class Null safety

Animated version of FractionallySizedBox which automatically transitions the child's size over a given duration whenever the given widthFactor or heightFactor changes, as well as the position whenever the given alignment changes.

For the animation, you can choose a curve as well as a duration and the widget will automatically animate to the new target widthFactor or heightFactor.

The following example transitions an AnimatedFractionallySizedBox between two states. It adjusts the heightFactor, widthFactor, and alignment properties when tapped, using a curve of Curves.fastOutSlowIn
To create a local project with this code sample, run:
flutter create --sample=widgets.AnimatedFractionallySizedBox.1 mysample

See also:

  • AnimatedAlign, which is an implicitly animated version of Align.
  • AnimatedContainer, which can transition more values at once.
  • AnimatedSlide, which can animate the translation of child by a given offset relative to its size.
  • AnimatedPositioned, which, as a child of a Stack, automatically transitions its child's position over a given duration whenever the given position changes.


AnimatedFractionallySizedBox({Key? key, AlignmentGeometry alignment =, Widget? child, double? heightFactor, double? widthFactor, Curve curve = Curves.linear, required Duration duration, VoidCallback? onEnd})
Creates a widget that sizes its child to a fraction of the total available space that animates implicitly, and positions its child by an alignment that animates implicitly.


alignment AlignmentGeometry
How to align the child.
child Widget?
The widget below this widget in the tree.
curve Curve
The curve to apply when animating the parameters of this container.
final, inherited
duration Duration
The duration over which to animate the parameters of this container.
final, inherited
hashCode int
The hash code for this object.
@nonVirtual, read-only, inherited
heightFactor double?
If non-null, the fraction of the incoming height given to the child.
key Key?
Controls how one widget replaces another widget in the tree.
final, inherited
onEnd VoidCallback?
Called every time an animation completes.
final, inherited
runtimeType Type
A representation of the runtime type of the object.
read-only, inherited
widthFactor double?
If non-null, the fraction of the incoming width given to the child.


createElement() StatefulElement
Creates a StatefulElement to manage this widget's location in the tree.
createState() AnimatedWidgetBaseState<AnimatedFractionallySizedBox>
Creates the mutable state for this widget at a given location in the tree.
debugDescribeChildren() List<DiagnosticsNode>
Returns a list of DiagnosticsNode objects describing this node's children.
@protected, inherited
debugFillProperties(DiagnosticPropertiesBuilder properties) → void
Add additional properties associated with the node.
noSuchMethod(Invocation invocation) → dynamic
Invoked when a non-existent method or property is accessed.
toDiagnosticsNode({String? name, DiagnosticsTreeStyle? style}) DiagnosticsNode
Returns a debug representation of the object that is used by debugging tools and by DiagnosticsNode.toStringDeep.
toString({DiagnosticLevel minLevel =}) String
A string representation of this object.
toStringDeep({String prefixLineOne = '', String? prefixOtherLines, DiagnosticLevel minLevel = DiagnosticLevel.debug}) String
Returns a string representation of this node and its descendants.
toStringShallow({String joiner = ', ', DiagnosticLevel minLevel = DiagnosticLevel.debug}) String
Returns a one-line detailed description of the object.
toStringShort() String
A short, textual description of this widget.


operator ==(Object other) bool
The equality operator.
@nonVirtual, inherited