Viewport class Null safety
A widget that is bigger on the inside.
Viewport is the visual workhorse of the scrolling machinery. It displays a subset of its children according to its own dimensions and the given offset. As the offset varies, different children are visible through the viewport.
Viewport hosts a bidirectional list of slivers, anchored on a center sliver, which is placed at the zero scroll offset. The center widget is displayed in the viewport according to the anchor property.
Slivers that are earlier in the child list than center are displayed in reverse order in the reverse axisDirection starting from the center. For example, if the axisDirection is AxisDirection.down, the first sliver before center is placed above the center. The slivers that are later in the child list than center are placed in order in the axisDirection. For example, in the preceding scenario, the first sliver after center is placed below the center.
Viewport cannot contain box children directly. Instead, use a SliverList, SliverFixedExtentList, SliverGrid, or a SliverToBoxAdapter, for example.
See also:
- ListView, PageView, GridView, and CustomScrollView, which combine Scrollable and Viewport into widgets that are easier to use.
- SliverToBoxAdapter, which allows a box widget to be placed inside a sliver context (the opposite of this widget).
- ShrinkWrappingViewport, a variant of Viewport that shrink-wraps its contents along the main axis.
- ViewportElementMixin, which should be mixed in to the Element type used by viewport-like widgets to correctly handle scroll notifications.
- Inheritance
- Implementers
Constructors
-
Viewport({Key? key, AxisDirection axisDirection = AxisDirection.down, AxisDirection? crossAxisDirection, double anchor = 0.0, required ViewportOffset offset, Key? center, double? cacheExtent, CacheExtentStyle cacheExtentStyle = CacheExtentStyle.pixel, Clip clipBehavior = Clip.hardEdge, List<
Widget> slivers = const <Widget>[]}) - Creates a widget that is bigger on the inside.
Properties
- anchor → double
-
The relative position of the zero scroll offset.
final
- axisDirection → AxisDirection
-
The direction in which the offset's ViewportOffset.pixels increases.
final
- cacheExtent → double?
-
The viewport has an area before and after the visible area to cache items
that are about to become visible when the user scrolls.
final
- cacheExtentStyle → CacheExtentStyle
-
Controls how the cacheExtent is interpreted.
final
- center → Key?
-
The first child in the GrowthDirection.forward growth direction.
final
-
children
→ List<
Widget> -
The widgets below this widget in the tree.
finalinherited
- clipBehavior → Clip
-
The content will be clipped (or not) according to this option.
final
- crossAxisDirection → AxisDirection?
-
The direction in which child should be laid out in the cross axis.
final
- hashCode → int
- The hash code for this object.
- key → Key?
-
Controls how one widget replaces another widget in the tree.
finalinherited
- offset → ViewportOffset
-
Which part of the content inside the viewport should be visible.
final
- runtimeType → Type
-
A representation of the runtime type of the object.
read-onlyinherited
Methods
-
createElement(
) → MultiChildRenderObjectElement -
RenderObjectWidgets always inflate to a RenderObjectElement subclass.
override
-
createRenderObject(
BuildContext context) → RenderViewport -
Creates an instance of the RenderObject class that this
RenderObjectWidget represents, using the configuration described by this
RenderObjectWidget.
override
-
debugDescribeChildren(
) → List< DiagnosticsNode> -
Returns a list of
DiagnosticsNode
objects describing this node's children.protected">@protectedinherited -
debugFillProperties(
DiagnosticPropertiesBuilder properties) → void -
Add additional properties associated with the node.
override
-
didUnmountRenderObject(
covariant RenderObject renderObject) → void -
A render object previously associated with this widget has been removed
from the tree. The given RenderObject will be of the same type as
returned by this object's createRenderObject.
protected">@protectedinherited
-
noSuchMethod(
Invocation invocation) → dynamic -
Invoked when a non-existent method or property is accessed.
inherited
-
toDiagnosticsNode(
{String? name, DiagnosticsTreeStyle? style}) → DiagnosticsNode -
Returns a debug representation of the object that is used by debugging
tools and by DiagnosticsNode.toStringDeep.
inherited
-
toString(
{DiagnosticLevel minLevel = DiagnosticLevel.info}) → String -
A string representation of this object.
inherited
-
toStringDeep(
{String prefixLineOne = '', String? prefixOtherLines, DiagnosticLevel minLevel = DiagnosticLevel.debug}) → String -
Returns a string representation of this node and its descendants.
inherited
-
toStringShallow(
{String joiner = ', ', DiagnosticLevel minLevel = DiagnosticLevel.debug}) → String -
Returns a one-line detailed description of the object.
inherited
-
toStringShort(
) → String -
A short, textual description of this widget.
inherited
-
updateRenderObject(
BuildContext context, covariant RenderViewport renderObject) → void -
Copies the configuration described by this RenderObjectWidget to the
given RenderObject, which will be of the same type as returned by this
object's createRenderObject.
override
Operators
-
operator ==(
Object other) → bool -
The equality operator.
nonVirtual">@nonVirtualinherited
Static Methods
-
getDefaultCrossAxisDirection(
BuildContext context, AxisDirection axisDirection) → AxisDirection - Given a BuildContext and an AxisDirection, determine the correct cross axis direction.