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:



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.


anchor double
The relative position of the zero scroll offset.
axisDirection AxisDirection
The direction in which the offset's ViewportOffset.pixels increases.
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.
cacheExtentStyle CacheExtentStyle
Controls how the cacheExtent is interpreted.
center Key?
The first child in the GrowthDirection.forward growth direction.
children List<Widget>
The widgets below this widget in the tree.
final, inherited
clipBehavior Clip
The content will be clipped (or not) according to this option.
crossAxisDirection AxisDirection?
The direction in which child should be laid out in the cross axis.
hashCode int
The hash code for this object.
@nonVirtual, read-only, inherited
key Key?
Controls how one widget replaces another widget in the tree.
final, inherited
offset ViewportOffset
Which part of the content inside the viewport should be visible.
runtimeType Type
A representation of the runtime type of the object.
read-only, inherited


createElement() MultiChildRenderObjectElement
RenderObjectWidgets always inflate to a RenderObjectElement subclass.
createRenderObject(BuildContext context) RenderViewport
Creates an instance of the RenderObject class that this RenderObjectWidget represents, using the configuration described by this RenderObjectWidget.
debugDescribeChildren() List<DiagnosticsNode>
Returns a list of DiagnosticsNode objects describing this node's children.
@protected, inherited
debugFillProperties(DiagnosticPropertiesBuilder properties) → void
Add additional properties associated with the node.
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, inherited
noSuchMethod(Invocation invocation) → dynamic
Invoked when a non-existent method or property is accessed.
toDiagnosticsNode({String? name, DiagnosticsTreeStyle? style}) DiagnosticsNode
Returns a debug representation of the object that is used by debugging tools and by DiagnosticsNode.toStringDeep.
toString({DiagnosticLevel minLevel =}) String
A string representation of this object.
toStringDeep({String prefixLineOne = '', String? prefixOtherLines, DiagnosticLevel minLevel = DiagnosticLevel.debug}) String
Returns a string representation of this node and its descendants.
toStringShallow({String joiner = ', ', DiagnosticLevel minLevel = DiagnosticLevel.debug}) String
Returns a one-line detailed description of the object.
toStringShort() String
A short, textual description of this widget.
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.


operator ==(Object other) bool
The equality operator.
@nonVirtual, inherited

Static Methods

getDefaultCrossAxisDirection(BuildContext context, AxisDirection axisDirection) AxisDirection
Given a BuildContext and an AxisDirection, determine the correct cross axis direction.