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 and updateShouldRebuild returns true.
• 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.

In the event that an ancestor skips the layout of this subtree so the constraints become outdated, the builder rebuilds with the last known constraints.

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.

See also:

• SliverLayoutBuilder, the sliver counterpart of this widget.
• Builder, which calls a builder function at build time.
• StatefulBuilder, which passes its builder function a setState callback.
• CustomSingleChildLayout, which positions its child during layout.
• The catalog of layout widgets.

Inheritance

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

Constructors

LayoutBuilder({Key? key, required Widget builder(BuildContext context, BoxConstraints constraints)})

Creates a widget that defers its building until layout.

const

Properties

builder → Widget Function(BuildContext context, BoxConstraints constraints)

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 a RenderObjectElement subclass.

inherited

createRenderObject(BuildContext context) → RenderAbstractLayoutBuilderMixin<BoxConstraints, RenderBox>

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.

inherited

debugFillProperties(DiagnosticPropertiesBuilder properties) → void

Add additional properties associated with the node.

inherited

didUnmountRenderObject(covariant RenderObject renderObject) → void

This method is called when a RenderObject that was previously associated with this widget is removed from the render tree. The provided RenderObject will be of the same type as the one created by this widget's createRenderObject method.

inherited

noSuchMethod(Invocation invocation) → 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 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, int wrapWidth = 65}) → 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.

inherited

updateShouldRebuild(covariant AbstractLayoutBuilder<BoxConstraints> oldWidget) → bool

Whether builder needs to be called again even if the layout constraints are the same.

inherited

Operators

operator ==(Object other) → bool

The equality operator.

inherited