NullableIndexedWidgetBuilder typedef Null safety

Widget? NullableIndexedWidgetBuilder (
  1. BuildContext context,
  2. int index
)

Signature for a function that creates a widget for a given index, e.g., in a list, but may return null.

Used by SliverChildBuilderDelegate.builder and other APIs that use lazily-generated widgets where the child count is not known ahead of time.

Unlike most builders, this callback can return null, indicating the index is out of range. Whether and when this is valid depends on the semantics of the builder. For example, SliverChildBuilderDelegate.builder returns null when the index is out of range, where the range is defined by the SliverChildBuilderDelegate.childCount; so in that case the index parameter's value may determine whether returning null is valid or not.

See also:

Implementation

typedef NullableIndexedWidgetBuilder = Widget? Function(BuildContext context, int index);