TwoDimensionalChildDelegate class abstract

A delegate that supplies children for scrolling in two dimensions.

A TwoDimensionalScrollView lazily constructs its box children to avoid creating more children than are visible through the TwoDimensionalViewport. Rather than receiving children as an explicit List, it receives its children using a TwoDimensionalChildDelegate.

As a ChangeNotifier, this delegate allows subclasses to notify its listeners (typically as a subclass of RenderTwoDimensionalViewport) to rebuild when aspects of the delegate change. When values returned by getters or builders on this delegate change, notifyListeners should be called. This signals to the RenderTwoDimensionalViewport that the getters and builders need to be re-queried to update the layout of children in the viewport.

See also:



Creates a delegate that supplies children for scrolling in two dimensions.


hashCode int
The hash code for this object.
no setterinherited
hasListeners bool
Whether any listeners are currently registered.
no setterinherited
runtimeType Type
A representation of the runtime type of the object.
no setterinherited


addListener(VoidCallback listener) → void
Register a closure to be called when the object changes.
build(BuildContext context, covariant ChildVicinity vicinity) Widget?
Returns the child with the given ChildVicinity, which is described in terms of x and y indices.
dispose() → void
Discards any resources used by the object. After this is called, the object is not in a usable state and should be discarded (calls to addListener will throw after the object is disposed).
noSuchMethod(Invocation invocation) → dynamic
Invoked when a nonexistent method or property is accessed.
notifyListeners() → void
Call all the registered listeners.
removeListener(VoidCallback listener) → void
Remove a previously registered closure from the list of closures that are notified when the object changes.
shouldRebuild(covariant TwoDimensionalChildDelegate oldDelegate) bool
Called whenever a new instance of the child delegate class is provided.
toString() String
A string representation of this object.


operator ==(Object other) bool
The equality operator.