Widget class - widgets library (original) (raw)

Describes the configuration for an Element.

Widgets are the central class hierarchy in the Flutter framework. A widget is an immutable description of part of a user interface. Widgets can be inflated into elements, which manage the underlying render tree.

Widgets themselves have no mutable state (all their fields must be final). If you wish to associate mutable state with a widget, consider using aStatefulWidget, which creates a State object (viaStatefulWidget.createState) whenever it is inflated into an element and incorporated into the tree.

A given widget can be included in the tree zero or more times. In particular a given widget can be placed in the tree multiple times. Each time a widget is placed in the tree, it is inflated into an Element, which means a widget that is incorporated into the tree multiple times will be inflated multiple times.

The key property controls how one widget replaces another widget in the tree. If the runtimeType and key properties of the two widgets areoperator==, respectively, then the new widget replaces the old widget by updating the underlying element (i.e., by calling Element.update with the new widget). Otherwise, the old element is removed from the tree, the new widget is inflated into an element, and the new element is inserted into the tree.

See also:

• StatefulWidget and State, for widgets that can build differently several times over their lifetime.
• InheritedWidget, for widgets that introduce ambient state that can be read by descendant widgets.
• StatelessWidget, for widgets that always build the same way given a particular configuration and ambient state.

Inheritance

• Object
• DiagnosticableTree
• Widget

Implementers

• PreferredSizeWidget
• ProxyWidget
• RenderObjectWidget
• RootWidget
• StatefulWidget
• StatelessWidget
• ViewCollection

Annotations

• @immutable

Constructors

Widget({Key? key})

Initializes key for subclasses.

const

Properties

hashCode → int

The hash code for this object.

no setteroverride

key → Key?

Controls how one widget replaces another widget in the tree.

final

runtimeType → Type

A representation of the runtime type of the object.

no setterinherited

Methods

createElement()→ Element

Inflates this configuration to a concrete instance.

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.

override

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.

override

Operators

operator ==(Object other)→ bool

The equality operator.

override

Static Methods

canUpdate(Widget oldWidget, Widget newWidget)→ bool

Whether the newWidget can be used to update an Element that currently has the oldWidget as its configuration.