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

Similar to theBuilder widget except that the framework calls thebuilderfunction at layout time and provides the parent widget's constraints. Thisis useful when the parent constrains the child's size and doesn't depend onthe child's intrinsic size. TheLayoutBuilder's final size will match itschild's size.

Thebuilder 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 andupdateShouldRebuild returnstrue.
• When the dependencies that thebuilder function subscribes to change.

Thebuilder function isnot called during layout if the parent passesthe same constraints repeatedly.

In the event that an ancestor skips the layout of this subtree so theconstraints become outdated, thebuilder rebuilds with the last knownconstraints.

If the child should be smaller than the parent, consider wrapping the childin anAlign widget. If the child might want to be bigger, considerwrapping it in aSingleChildScrollView orOverflowBox.

See also:

• SliverLayoutBuilder, the sliver counterpart of this widget.
• Builder, which calls abuilder function at build time.
• StatefulBuilder, which passes itsbuilder function asetState callback.
• CustomSingleChildLayout, which positions its child during layout.
• Thecatalog of layout widgets.

Inheritance

• Object
• DiagnosticableTree
• Widget
• RenderObjectWidget
• AbstractLayoutBuilder<BoxConstraints>
• ConstrainedLayoutBuilder<BoxConstraints>
• LayoutBuilder

Constructors

LayoutBuilder({Key?key,requiredWidgetbuilder(BuildContextcontext,BoxConstraintsconstraints)})

Creates a widget that defers its building until layout.

const

Properties

builder→Widget Function(BuildContextcontext,BoxConstraintsconstraints)

Called at layout time to construct the widget tree.

finalinherited

hashCode→int

The hash code for this object.

no setterinherited

key→Key?

Controls how one widget replaces another widget in the tree.

finalinherited

runtimeType→Type

A representation of the runtime type of the object.

no setterinherited

Methods

createElement()→RenderObjectElement

RenderObjectWidgets always inflate to aRenderObjectElement subclass.

inherited

createRenderObject(BuildContextcontext)→RenderAbstractLayoutBuilderMixin<BoxConstraints,RenderBox>

Creates an instance of theRenderObject class that thisRenderObjectWidget represents, using the configuration described by thisRenderObjectWidget.

override

debugDescribeChildren()→List<DiagnosticsNode>

Returns a list ofDiagnosticsNode objects describing this node'schildren.

inherited

debugFillProperties(DiagnosticPropertiesBuilderproperties)→ void

Add additional properties associated with the node.

inherited

didUnmountRenderObject(covariantRenderObjectrenderObject)→ void

This method is called when a RenderObject that was previouslyassociated with this widget is removed from the render tree.The providedRenderObject will be of the same type as the one created bythis widget'screateRenderObject method.

inherited

noSuchMethod(Invocationinvocation)→ dynamic

Invoked when a nonexistent method or property is accessed.

inherited

toDiagnosticsNode({String?name,DiagnosticsTreeStyle?style})→DiagnosticsNode

Returns a debug representation of the object that is used by debuggingtools and byDiagnosticsNode.toStringDeep.

inherited

toString({DiagnosticLevelminLevel =DiagnosticLevel.info})→String

A string representation of this object.

inherited

toStringDeep({StringprefixLineOne ='',String?prefixOtherLines,DiagnosticLevelminLevel =DiagnosticLevel.debug,intwrapWidth =65})→String

Returns a string representation of this node and its descendants.

inherited

toStringShallow({Stringjoiner =', ',DiagnosticLevelminLevel =DiagnosticLevel.debug})→String

Returns a one-line detailed description of the object.

inherited

toStringShort()→String

A short, textual description of this widget.

inherited

updateRenderObject(BuildContextcontext,covariantRenderObjectrenderObject)→ void

Copies the configuration described by thisRenderObjectWidget to thegivenRenderObject, which will be of the same type as returned by thisobject'screateRenderObject.

inherited

updateShouldRebuild(covariantAbstractLayoutBuilder<BoxConstraints>oldWidget)→bool

Whetherbuilder needs to be called again even if the layout constraintsare the same.

inherited

Operators

operator ==(Objectother)→bool

The equality operator.

inherited