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;

  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;

  Type get debugTypicalAncestorWidgetClass => FrogJar;

See also:



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.


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. [...]
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


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. [...]
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. [...]
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. [...]
toDiagnosticsNode({String? name, DiagnosticsTreeStyle? style}) DiagnosticsNode
Returns a debug representation of the object that is used by debugging tools and by DiagnosticsNode.toStringDeep. [...]
toString({DiagnosticLevel minLevel =}) String
A string representation of this object. [...]
toStringDeep({String prefixLineOne = '', String? prefixOtherLines, DiagnosticLevel minLevel = DiagnosticLevel.debug}) String
Returns a string representation of this node and its descendants. [...]
toStringShallow({String joiner = ', ', DiagnosticLevel minLevel = DiagnosticLevel.debug}) String
Returns a one-line detailed description of the object. [...]
toStringShort() String
A short, textual description of this widget.


operator ==(Object other) bool
The equality operator. [...]
@nonVirtual, inherited