SizedBox class - widgets library

A box with a specified size.

If given a child, this widget forces it to have a specific width and/or height. These values will be ignored if this widget's parent does not permit them. For example, this happens if the parent is the screen (forces the child to be the same size as the parent), or another SizedBox (forces its child to have a specific width and/or height). This can be remedied by wrapping the child SizedBox in a widget that does permit it to be any size up to the size of the parent, such as Center or Align.

If either the width or height is null, this widget will try to size itself to match the child's size in that dimension. If the child's size depends on the size of its parent, the height and width must be provided.

If not given a child, SizedBox will try to size itself as close to the specified height and width as possible given the parent's constraints. If height or width is null or unspecified, it will be treated as zero.

The SizedBox.expand constructor can be used to make a SizedBox that sizes itself to fit the parent. It is equivalent to setting width and height to double.infinity.

const SizedBox(
  width: 200.0,
  height: 300.0,
  child: Card(child: Text('Hello World!')),
)

See also:

• ConstrainedBox, a more generic version of this class that takes arbitrary BoxConstraints instead of an explicit width and height.
• UnconstrainedBox, a container that tries to let its child draw without constraints.
• FractionallySizedBox, a widget that sizes its child to a fraction of the total available space.
• AspectRatio, a widget that attempts to fit within the parent's constraints while also sizing its child to match a given aspect ratio.
• FittedBox, which sizes and positions its child widget to fit the parent according to a given BoxFit discipline.
• The catalog of layout widgets.
• Understanding constraints, an in-depth article about layout in Flutter.

Inheritance

• Object
• DiagnosticableTree
• Widget
• RenderObjectWidget
• SingleChildRenderObjectWidget
• SizedBox

Constructors

SizedBox({Key? key, double? width, double? height, Widget? child})

Creates a fixed size box. The width and height parameters can be null to indicate that the size of the box should not be constrained in the corresponding dimension.

const

SizedBox.expand({Key? key, Widget? child})

Creates a box that will become as large as its parent allows.

const

SizedBox.fromSize({Key? key, Widget? child, Size? size})

Creates a box with the specified size.

SizedBox.shrink({Key? key, Widget? child})

Creates a box that will become as small as its parent allows.

const

SizedBox.square({Key? key, Widget? child, double? dimension})

Creates a box whose width and height are equal.

const

Properties

child → Widget?

The widget below this widget in the tree.

final, inherited

hashCode → int

The hash code for this object.

height → double?

If non-null, requires the child to have exactly this height.

final

key → Key?

Controls how one widget replaces another widget in the tree.

final, inherited

runtimeType → Type

A representation of the runtime type of the object.

read-only, inherited

width → double?

If non-null, requires the child to have exactly this width.

final

Methods

createElement() → SingleChildRenderObjectElement

RenderObjectWidgets always inflate to a RenderObjectElement subclass.

inherited

createRenderObject(BuildContext context) → RenderConstrainedBox

Creates an instance of the RenderObject class that this RenderObjectWidget represents, using the configuration described by this RenderObjectWidget.

override

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.

override

didUnmountRenderObject(covariant RenderObject renderObject) → void

A render object previously associated with this widget has been removed from the tree. The given RenderObject will be of the same type as returned by this object's createRenderObject.

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.

override

updateRenderObject(BuildContext context, covariant RenderConstrainedBox renderObject) → void

Copies the configuration described by this RenderObjectWidget to the given RenderObject, which will be of the same type as returned by this object's createRenderObject.

override

Operators

operator ==(Object other) → bool

The equality operator.