NullableStatefulWidget class abstract

A widget that has mutable state and whose NullableState.nullableBuild may return null.

When NullableState.nullableBuild returns null, a collapsed placeholder is used that occupies zero space. StreamRow and StreamColumn skip collapsed children when calculating spacing, so the widget is effectively invisible.

{@tool snippet}

A counter badge that hides itself when the count is zero:

class CountBadge extends NullableStatefulWidget {
  const CountBadge({super.key});

  @override
  NullableState<CountBadge> createState() => _CountBadgeState();
}

class _CountBadgeState extends NullableState<CountBadge> {
  int _count = 0;

  @override
  Widget? nullableBuild(BuildContext context) {
    if (_count == 0) return null;
    return Text('$_count');
  }
}

{@end-tool}

See also:

• NullableStatelessWidget, for a stateless variant.
• NullableBuilder, for inline nullable children without a subclass.
• NullableState, the State subclass to use with this widget.

Inheritance

• Object
• DiagnosticableTree
• Widget
• StatefulWidget
• NullableStatefulWidget

Constructors

NullableStatefulWidget({Key? key})

Creates a nullable stateful widget.

const

Properties

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

runtimeType → Type

A representation of the runtime type of the object.

no setter, inherited

Methods

createElement() → StatefulElement

Creates a StatefulElement to manage this widget's location in the tree.

inherited

createState() → NullableState<NullableStatefulWidget>

Creates the mutable state for this widget at a given location in the tree.

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

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