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:

• TwoDimensionalChildBuilderDelegate, an concrete subclass of this that lazily builds children on demand.
• TwoDimensionalChildListDelegate, an concrete subclass of this that uses a two dimensional array to layout children.