Viewport class

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.

Constructors

Viewport({Key key, AxisDirection axisDirection: AxisDirection.down, AxisDirection crossAxisDirection, double anchor: 0.0, @required ViewportOffset offset, Key center, double cacheExtent, List<Widget> slivers: const [] }): 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
center → Key: The first child in the GrowthDirection.forward growth direction. [...]
final
crossAxisDirection → AxisDirection: The direction in which child should be laid out in the cross axis. [...]
final
offset → ViewportOffset: Which part of the content inside the viewport should be visible. [...]
final
children → List<Widget>: The widgets below this widget in the tree. [...]
final, inherited
hashCode → int: The hash code for this object. [...]
read-only, inherited
key → Key: Controls how one widget replaces another widget in the tree. [...]
final, inherited
runtimeType → Type: A representation of the runtime type of the object.
read-only, inherited

Methods

createElement() → _ViewportElement: 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
debugFillProperties(DiagnosticPropertiesBuilder properties) → void: Add additional properties associated with the node. [...]
override
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
debugDescribeChildren() → List<DiagnosticsNode>: Returns a list of DiagnosticsNode objects describing this node's children. [...]
@protected, inherited
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. [...]
inherited
toDiagnosticsNode({String name, DiagnosticsTreeStyle style }) → DiagnosticsNode: Returns a debug representation of the object that is used by debugging tools and by toStringDeep. [...]
inherited
toString({DiagnosticLevel minLevel: DiagnosticLevel.debug }) → String: Returns 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

Operators

operator ==(dynamic other) → bool: The equality operator. [...]
inherited

Static Methods

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