ListView.builder constructor
Creates a scrollable, linear array of widgets that are created on demand.
This constructor is appropriate for list 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 ListView to
estimate the maximum scroll extent.
The itemBuilder
callback will be called only with indices greater than
or equal to zero and less than itemCount
.
The itemBuilder
should actually create the widget instances when called.
Avoid using a builder that returns a previously-constructed widget; if the
list view's children are created in advance, or all at once when the
ListView itself is created, it is more efficient to use new ListView.
Even more efficient, however, is to create the instances on demand using
this constructor's itemBuilder
callback.
The addAutomaticKeepAlives
argument corresponds to the
SliverChildBuilderDelegate.addAutomaticKeepAlives property. The
addRepaintBoundaries
argument corresponds to the
SliverChildBuilderDelegate.addRepaintBoundaries property. The
addSemanticIndexes
argument corresponds to the
SliverChildBuilderDelegate.addSemanticIndexes property. None may be
null.
Implementation
ListView.builder({
Key key,
Axis scrollDirection = Axis.vertical,
bool reverse = false,
ScrollController controller,
bool primary,
ScrollPhysics physics,
bool shrinkWrap = false,
EdgeInsetsGeometry padding,
this.itemExtent,
@required IndexedWidgetBuilder itemBuilder,
int itemCount,
bool addAutomaticKeepAlives = true,
bool addRepaintBoundaries = true,
bool addSemanticIndexes = true,
double cacheExtent,
int semanticChildCount,
}) : childrenDelegate = SliverChildBuilderDelegate(
itemBuilder,
childCount: itemCount,
addAutomaticKeepAlives: addAutomaticKeepAlives,
addRepaintBoundaries: addRepaintBoundaries,
addSemanticIndexes: addSemanticIndexes,
), super(
key: key,
scrollDirection: scrollDirection,
reverse: reverse,
controller: controller,
primary: primary,
physics: physics,
shrinkWrap: shrinkWrap,
padding: padding,
cacheExtent: cacheExtent,
semanticChildCount: semanticChildCount ?? itemCount,
);