ParentDataWidget<T extends RenderObjectWidget> class

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 RenderObject, and thus also to a particular RenderObjectWidget class. That class is T, the ParentDataWidget type argument.

Sample code

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<FrogJar> {
    Key key,
    @required this.size,
    @required Widget child,
  }) : assert(child != null),
       assert(size != null),
       super(key: key, child: child);

  final Size size;

  void applyParentData(RenderObject renderObject) {
    final FrogJarParentData parentData = renderObject.parentData;
    if (parentData.size != size) {
      parentData.size = size;
      final RenderFrogJar targetParent = renderObject.parent;

See also:

Implemented by


ParentDataWidget({Key key, 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
hashCode int
The hash code for this object. [...]
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. [...]
debugDescribeInvalidAncestorChain({String description, String ownershipChain, bool foundValidAncestor, Iterable<Widget> badAncestors }) String
Subclasses should override this to describe the requirements for using the ParentDataWidget subclass. It is called when debugIsValidAncestor() returned false for an ancestor, or when there are extraneous ParentDataWidgets in the ancestor chain.
debugIsValidAncestor(RenderObjectWidget ancestor) bool
Subclasses should override this method to return true if the given ancestor is a RenderObjectWidget that wraps a RenderObject that can handle the kind of ParentData widget that the ParentDataWidget subclass handles. [...]
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. [...]
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 toStringDeep. [...]
toString({DiagnosticLevel minLevel: DiagnosticLevel.debug }) String
Returns 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 ==(dynamic other) bool
The equality operator. [...]