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.
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> {
FrogSize({
Key key,
@required this.size,
@required Widget child,
}) : assert(child != null),
assert(size != null),
super(key: key, child: child);
final Size size;
@override
void applyParentData(RenderObject renderObject) {
final FrogJarParentData parentData = renderObject.parentData;
if (parentData.size != size) {
parentData.size = size;
final RenderFrogJar targetParent = renderObject.parent;
targetParent.markNeedsLayout();
}
}
}
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.
- RenderObjectWidget, the class for widgets that wrap RenderObjects.
The
T
type parameter for ParentDataWidget is a RenderObjectWidget. - StatefulWidget and State, for widgets that can build differently several times over their lifetime.
- Inheritance
- Object
- Diagnosticable
- DiagnosticableTree
- Widget
- ProxyWidget
- ParentDataWidget
- Implementers
Constructors
- 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.
const
Properties
- 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
Methods
-
applyParentData(
RenderObject renderObject) → void -
Write the data from this widget into the given render object's parent data. [...]
@protected
-
createElement(
) → ParentDataElement< T> -
Inflates this configuration to a concrete instance. [...]
override
-
debugCanApplyOutOfTurn(
) → bool -
Whether the ParentDataElement.applyWidgetOutOfTurn method is allowed
with this widget. [...]
@protected
-
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. [...]
inherited
-
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 toStringDeep. [...]
inherited
-
toString(
{DiagnosticLevel minLevel: DiagnosticLevel.debug }) → String -
Returns 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 ==(
dynamic other) → bool -
The equality operator. [...]
inherited