SizeTransition class

Animates its own size and clips and aligns its child.

SizeTransition acts as a ClipRect that animates either its width or its height, depending upon the value of axis. The alignment of the child along the axis is specified by the axisAlignment.

Like most widgets, SizeTransition will conform to the constraints it is given, so be sure to put it in a context where it can change size. For instance, if you place it into a Container with a fixed size, then the SizeTransition will not be able to change size, and will appear to do nothing.

Here's an illustration of the SizeTransition widget, with it's sizeFactor animated by a CurvedAnimation set to Curves.fastOutSlowIn:

This code defines a widget that uses SizeTransition to change the size of FlutterLogo continually. It is built with a Scaffold where the internal widget has space to change its size.

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

See also:

  • AnimatedCrossFade, for a widget that automatically animates between the sizes of two children, fading between them.
  • ScaleTransition, a widget that scales the size of the child instead of clipping it.
  • PositionedTransition, a widget that animates its child from a start position to an end position over the lifetime of the animation.
  • RelativePositionedTransition, a widget that transitions its child's position based on the value of a rectangle relative to a bounding box.


SizeTransition({Key? key, Axis axis = Axis.vertical, required Animation<double> sizeFactor, double axisAlignment = 0.0, double? fixedCrossAxisSizeFactor, Widget? child})
Creates a size transition.


axis Axis
Axis.horizontal if sizeFactor modifies the width, otherwise Axis.vertical.
axisAlignment double
Describes how to align the child along the axis that sizeFactor is modifying.
child Widget?
The widget below this widget in the tree.
fixedCrossAxisSizeFactor double?
The factor by which to multiply the cross axis size of the child.
hashCode int
The hash code for this object.
no setterinherited
key Key?
Controls how one widget replaces another widget in the tree.
listenable Listenable
The Listenable to which this widget is listening.
runtimeType Type
A representation of the runtime type of the object.
no setterinherited
sizeFactor Animation<double>
The animation that controls the (clipped) size of the child.
no setter


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).
createElement() StatefulElement
Creates a StatefulElement to manage this widget's location in the tree.
createState() State<AnimatedWidget>
Subclasses typically do not override this method.
debugDescribeChildren() List<DiagnosticsNode>
Returns a list of DiagnosticsNode objects describing this node's children.
debugFillProperties(DiagnosticPropertiesBuilder properties) → void
Add additional properties associated with the node.
noSuchMethod(Invocation invocation) → dynamic
Invoked when a nonexistent 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.