BuilderModifier class

A stateless utility widget whose build method uses its builder callback to create the widget's child.

This widget is a simple inline alternative to defining a StatelessWidget subclass. For example a widget defined and used like this:

class Foo extends StatelessWidget {
  @override
  Widget build(BuildContext context) => Text('foo');
}

Center(child: Foo())

Could equally well be defined and used like this, without defining a new widget class:

Center(
  child: Builder(
    builder: (BuildContext context) => Text('foo');
  ),
)

The difference between either of the previous examples and simply creating a child directly, without an intervening widget, is the extra BuildContext element that the additional widget adds. This is particularly noticeable when the tree contains an inherited widget that is referred to by a method like Scaffold.of, which visits the child widget's BuildContext ancestors.

In the following example the button's onPressed callback is unable to find the enclosing ScaffoldState with Scaffold.of:

Widget build(BuildContext context) {
  return Scaffold(
    body: Center(
      child: TextButton(
        onPressed: () {
          // Fails because Scaffold.of() doesn't find anything
          // above this widget's context.
          print(Scaffold.of(context).hasAppBar);
        },
        child: Text('hasAppBar'),
      )
    ),
  );
}

A Builder widget introduces an additional BuildContext element and so the Scaffold.of method succeeds.

Widget build(BuildContext context) {
  return Scaffold(
    body: Builder(
      builder: (BuildContext context) {
        return Center(
          child: TextButton(
            onPressed: () {
              print(Scaffold.of(context).hasAppBar);
            },
            child: Text('hasAppBar'),
          ),
        );
      },
    ),
  );
}

See also:

• StatefulBuilder, A stateful utility widget whose build method uses its builder callback to create the widget's child.

Inheritance

• Object
• DiagnosticableTree
• Widget
• StatelessWidget
• SingleChildStatelessModifier
• BuilderModifier

Available extensions

• ModifierTransformer

Constructors

BuilderModifier({Key? key, Key? modifierKey, Widget? child, required SingleChildWidgetBuilder builder})

Creates a widget that delegates its build to a callback.

const

Properties

builder → SingleChildWidgetBuilder

Called to obtain the child widget.

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

modified() → Modifier

Available on Widget, provided by the ModifierTransformer extension

Transform normal widget to Modifier

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

Operators

operator ==(Object other) → bool

The equality operator.

inherited