ParentDataWidget<T extends ParentData> class Null safety

Base class for widgets that hook ParentData information to children of RenderObjectWidgets.

This can be used to provide per-child configuration for RenderObjectWidgets with more than one child. For example, Stack uses the Positioned parent data widget to position each child.

A ParentDataWidget is specific to a particular kind of ParentData. That class is T, the ParentData type argument.

This example shows how you would build a ParentDataWidget to configure a FrogJar widget's children by specifying a Size for each one.
class FrogSize extends ParentDataWidget<FrogJarParentData> {
  const FrogSize({
    Key? key,
    required this.size,
    required Widget child,
  }) : super(key: key, child: child);

  final Size size;

  @override
  void applyParentData(RenderObject renderObject) {
    final FrogJarParentData parentData = renderObject.parentData! as FrogJarParentData;
    if (parentData.size != size) {
      parentData.size = size;
      final RenderFrogJar targetParent = renderObject.parent! as RenderFrogJar;
      targetParent.markNeedsLayout();
    }
  }

  @override
  Type get debugTypicalAncestorWidgetClass => FrogJar;
}

See also:

Inheritance
Implementers

Constructors

ParentDataWidget({Key? key, required Widget child})
Abstract const constructor. This constructor enables subclasses to provide const constructors so that they can be used in const expressions.
const

Properties

child Widget
The widget below this widget in the tree. [...]
final, inherited
debugTypicalAncestorWidgetClass Type
The RenderObjectWidget that is typically used to set up the ParentData that applyParentData will write to. [...]
read-only
hashCode int
The hash code for this object. [...]
@nonVirtual, read-only, 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.
read-only, inherited

Methods

applyParentData(RenderObject renderObject) → void
Write the data from this widget into the given render object's parent data. [...]
createElement() ParentDataElement<T>
Inflates this configuration to a concrete instance. [...]
override
debugCanApplyOutOfTurn() bool
Whether the ParentDataElement.applyWidgetOutOfTurn method is allowed with this widget. [...]
debugDescribeChildren() List<DiagnosticsNode>
Returns a list of DiagnosticsNode objects describing this node's children. [...]
@protected, inherited
debugFillProperties(DiagnosticPropertiesBuilder properties) → void
Add additional properties associated with the node. [...]
inherited
debugIsValidRenderObject(RenderObject renderObject) bool
Checks if this widget can apply its parent data to the provided renderObject. [...]
noSuchMethod(Invocation invocation) → dynamic
Invoked when a non-existent 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. [...]
@nonVirtual, inherited