ParentDataWidget<T extends ParentData> class abstract

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.

class FrogSize extends ParentDataWidget<FrogJarParentData> {
  const FrogSize({
    super.key,
    required this.size,
    required super.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:

• RenderObject, the superclass for layout algorithms.
• RenderObject.parentData, the slot that this class configures.
• ParentData, the superclass of the data that will be placed in RenderObject.parentData slots. The T type parameter for ParentDataWidget is a ParentData.
• RenderObjectWidget, the class for widgets that wrap RenderObjects.
• StatefulWidget and State, for widgets that can build differently several times over their lifetime.