PageView.builder constructor Null safety

PageView.builder(
  1. {Key? key,
  2. Axis scrollDirection,
  3. bool reverse,
  4. PageController? controller,
  5. ScrollPhysics? physics,
  6. bool pageSnapping,
  7. ValueChanged<int>? onPageChanged,
  8. required IndexedWidgetBuilder itemBuilder,
  9. int? itemCount,
  10. DragStartBehavior dragStartBehavior,
  11. bool allowImplicitScrolling,
  12. String? restorationId,
  13. Clip clipBehavior,
  14. ScrollBehavior? scrollBehavior,
  15. bool padEnds}
)

Creates a scrollable list that works page by page using widgets that are created on demand.

This constructor is appropriate for page views with a large (or infinite) number of children because the builder is called only for those children that are actually visible.

Providing a non-null itemCount lets the PageView compute the maximum scroll extent.

itemBuilder will be called only with indices greater than or equal to zero and less than itemCount.

PageView.builder by default does not support child reordering. If you are planning to change child order at a later time, consider using PageView or PageView.custom.

The allowImplicitScrolling parameter must not be null. If true, the PageView will participate in accessibility scrolling more like a ListView, where implicit scroll actions will move to the next page rather than into the contents of the PageView.

Implementation

PageView.builder({
  Key? key,
  this.scrollDirection = Axis.horizontal,
  this.reverse = false,
  PageController? controller,
  this.physics,
  this.pageSnapping = true,
  this.onPageChanged,
  required IndexedWidgetBuilder itemBuilder,
  int? itemCount,
  this.dragStartBehavior = DragStartBehavior.start,
  this.allowImplicitScrolling = false,
  this.restorationId,
  this.clipBehavior = Clip.hardEdge,
  this.scrollBehavior,
  this.padEnds = true,
}) : assert(allowImplicitScrolling != null),
     assert(clipBehavior != null),
     controller = controller ?? _defaultPageController,
     childrenDelegate = SliverChildBuilderDelegate(itemBuilder, childCount: itemCount),
     super(key: key);