LayoutBuilder class Null safety

Builds a widget tree that can depend on the parent widget's size.

Similar to the Builder widget except that the framework calls the builder function at layout time and provides the parent widget's constraints. This is useful when the parent constrains the child's size and doesn't depend on the child's intrinsic size. The LayoutBuilder's final size will match its child's size.

The builder function is called in the following situations:

  • The first time the widget is laid out.
  • When the parent widget passes different layout constraints.
  • When the parent widget updates this widget.
  • When the dependencies that the builder function subscribes to change.

The builder function is not called during layout if the parent passes the same constraints repeatedly.

If the child should be smaller than the parent, consider wrapping the child in an Align widget. If the child might want to be bigger, consider wrapping it in a SingleChildScrollView or OverflowBox.

link
This example uses a LayoutBuilder to build a different widget depending on the available width. Resize the DartPad window to see LayoutBuilder in action!
To create a local project with this code sample, run:
flutter create --sample=widgets.LayoutBuilder.1 mysample

See also:

Inheritance

Constructors

LayoutBuilder({Key? key, required Widget builder(BuildContext, BoxConstraints)})
Creates a widget that defers its building until layout.
const

Properties

builder → LayoutWidgetBuilder
Called at layout time to construct the widget tree.
read-onlyoverride
hashCode → int
The hash code for this object.
nonVirtual">@nonVirtualread-onlyinherited
key → Key?
Controls how one widget replaces another widget in the tree.
finalinherited
runtimeType → Type
A representation of the runtime type of the object.
read-onlyinherited

Methods

createElement() → RenderObjectElement
RenderObjectWidgets always inflate to a RenderObjectElement subclass.
inherited
createRenderObject(BuildContext context) → RenderObject
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.
protected">@protectedinherited
debugFillProperties(DiagnosticPropertiesBuilder properties) → void
Add additional properties associated with the node.
inherited
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.
protected">@protectedinherited
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
updateRenderObject(BuildContext context, covariant RenderObject 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.
protected">@protectedinherited

Operators

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