GridView.builder constructor Null safety
- {Key? key,
- Axis scrollDirection = Axis.vertical,
- bool reverse = false,
- ScrollController? controller,
- bool? primary,
- ScrollPhysics? physics,
- bool shrinkWrap = false,
- EdgeInsetsGeometry? padding,
- required SliverGridDelegate gridDelegate,
- required IndexedWidgetBuilder itemBuilder,
- ChildIndexGetter? findChildIndexCallback,
- int? itemCount,
- bool addAutomaticKeepAlives = true,
- bool addRepaintBoundaries = true,
- bool addSemanticIndexes = true,
- double? cacheExtent,
- int? semanticChildCount,
- DragStartBehavior dragStartBehavior = DragStartBehavior.start,
- ScrollViewKeyboardDismissBehavior keyboardDismissBehavior = ScrollViewKeyboardDismissBehavior.manual,
- String? restorationId,
- Clip clipBehavior = Clip.hardEdge}
Creates a scrollable, 2D array of widgets that are created on demand.
This constructor is appropriate for grid 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
improves the ability of the GridView to
estimate the maximum scroll extent.
itemBuilder
will be called only with indices greater than or equal to
zero and less than itemCount
.
The findChildIndexCallback
corresponds to the
SliverChildBuilderDelegate.findChildIndexCallback property. If null,
a child widget may not map to its existing RenderObject when the order
of children returned from the children builder changes.
This may result in state-loss. This callback needs to be implemented if
the order of the children may change at a later time.
The gridDelegate argument must not be null.
The addAutomaticKeepAlives
argument corresponds to the
SliverChildBuilderDelegate.addAutomaticKeepAlives property. The
addRepaintBoundaries
argument corresponds to the
SliverChildBuilderDelegate.addRepaintBoundaries property. Both must not
be null.
Implementation
GridView.builder({
super.key,
super.scrollDirection,
super.reverse,
super.controller,
super.primary,
super.physics,
super.shrinkWrap,
super.padding,
required this.gridDelegate,
required IndexedWidgetBuilder itemBuilder,
ChildIndexGetter? findChildIndexCallback,
int? itemCount,
bool addAutomaticKeepAlives = true,
bool addRepaintBoundaries = true,
bool addSemanticIndexes = true,
super.cacheExtent,
int? semanticChildCount,
super.dragStartBehavior,
super.keyboardDismissBehavior,
super.restorationId,
super.clipBehavior,
}) : assert(gridDelegate != null),
childrenDelegate = SliverChildBuilderDelegate(
itemBuilder,
findChildIndexCallback: findChildIndexCallback,
childCount: itemCount,
addAutomaticKeepAlives: addAutomaticKeepAlives,
addRepaintBoundaries: addRepaintBoundaries,
addSemanticIndexes: addSemanticIndexes,
),
super(
semanticChildCount: semanticChildCount ?? itemCount,
);