LayoutBuilderModifier class

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.

{@tool dartpad} This example uses a LayoutBuilder to build a different widget depending on the available width. Resize the DartPad window to see LayoutBuilder in action!

** See code in examples/api/lib/widgets/layout_builder/layout_builder.0.dart ** {@end-tool}

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
• StatelessWidget
• SingleChildStatelessModifier
• LayoutBuilderModifier

Available extensions

• ModifierTransformer

Constructors

LayoutBuilderModifier({Key? key, Widget? child, Key? modifierKey, required SingleChildLayoutWidgetBuilder builder})

Creates a widget that defers its building until layout.

const

Properties

builder → SingleChildLayoutWidgetBuilder

Called at layout time to construct the widget tree.

final

hashCode → int

The hash code for this object.

no setter, inherited

key → Key?

Controls how one widget replaces another widget in the tree.

final, inherited

modifierKey → Key?

The actual key of the widget, which Modifier wrapped

final, inherited

runtimeType → Type

A representation of the runtime type of the object.

no setter, inherited

Methods

build(BuildContext context) → Widget

Describes the part of the user interface represented by this widget.

inherited

buildWithChild(BuildContext context, Widget? child) → Widget

A build method that receives an extra child parameter.

override

createElement() → SingleChildStatelessElement

Create a SingleChildStatelessElement

inherited

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

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}) → 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

Operators

operator ==(Object other) → bool

The equality operator.

inherited