TwoDimensionalViewport class abstract

A widget through which a portion of larger content can be viewed, typically in combination with a TwoDimensionalScrollable.

TwoDimensionalViewport is the visual workhorse of the two dimensional scrolling machinery. It displays a subset of its children according to its own dimensions and the given horizontalOffset an verticalOffset. As the offsets vary, different children are visible through the viewport.

Subclasses must implement createRenderObject and updateRenderObject. Both of these methods require the render object to be a subclass of RenderTwoDimensionalViewport. This class will create its own RenderObjectElement which already implements the TwoDimensionalChildManager, which means subclasses should cast the BuildContext to provide as the child manager to the RenderTwoDimensionalViewport.

This is an example of a subclass implementation of TwoDimensionalViewport, SimpleTwoDimensionalViewport. The RenderSimpleTwoDimensionalViewport is a subclass of RenderTwoDimensionalViewport.
link 
class SimpleTwoDimensionalViewport extends TwoDimensionalViewport {
  const SimpleTwoDimensionalViewport({
    super.key,
    required super.verticalOffset,
    required super.verticalAxisDirection,
    required super.horizontalOffset,
    required super.horizontalAxisDirection,
    required super.delegate,
    required super.mainAxis,
    super.cacheExtent,
    super.clipBehavior = Clip.hardEdge,
  });

  @override
  RenderSimpleTwoDimensionalViewport createRenderObject(BuildContext context) {
    return RenderSimpleTwoDimensionalViewport(
      horizontalOffset: horizontalOffset,
      horizontalAxisDirection: horizontalAxisDirection,
      verticalOffset: verticalOffset,
      verticalAxisDirection: verticalAxisDirection,
      mainAxis: mainAxis,
      delegate: delegate,
      childManager: context as TwoDimensionalChildManager,
      cacheExtent: cacheExtent,
      clipBehavior: clipBehavior,
    );
  }

  @override
  void updateRenderObject(BuildContext context, RenderSimpleTwoDimensionalViewport renderObject) {
    renderObject
      ..horizontalOffset = horizontalOffset
      ..horizontalAxisDirection = horizontalAxisDirection
      ..verticalOffset = verticalOffset
      ..verticalAxisDirection = verticalAxisDirection
      ..mainAxis = mainAxis
      ..delegate = delegate
      ..cacheExtent = cacheExtent
      ..clipBehavior = clipBehavior;
  }
}

See also:

  • Viewport, the equivalent of this widget that scrolls in only one dimension.
Inheritance

Constructors

TwoDimensionalViewport({Key? key, required ViewportOffset verticalOffset, required AxisDirection verticalAxisDirection, required ViewportOffset horizontalOffset, required AxisDirection horizontalAxisDirection, required TwoDimensionalChildDelegate delegate, required Axis mainAxis, double? cacheExtent, Clip clipBehavior = Clip.hardEdge})
Creates a viewport for RenderBox objects that extend and scroll in both horizontal and vertical dimensions.
const

Properties

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
clipBehavior → Clip
The content will be clipped (or not) according to this option.
final
delegate → TwoDimensionalChildDelegate
A delegate that provides the children for the TwoDimensionalViewport.
final
hashCode → int
The hash code for this object.
no setterinherited
horizontalAxisDirection → AxisDirection
The direction in which the horizontalOffset's ViewportOffset.pixels increases.
final
horizontalOffset → ViewportOffset
Which part of the content inside the viewport should be visible in the horizontal axis.
final
key → Key?
Controls how one widget replaces another widget in the tree.
finalinherited
mainAxis → Axis
The main axis of the two.
final
runtimeType → Type
A representation of the runtime type of the object.
no setterinherited
verticalAxisDirection → AxisDirection
The direction in which the verticalOffset's ViewportOffset.pixels increases.
final
verticalOffset → ViewportOffset
Which part of the content inside the viewport should be visible in the vertical axis.
final

Methods

createElement() → RenderObjectElement
RenderObjectWidgets always inflate to a RenderObjectElement subclass.
override
createRenderObject(BuildContext context) → RenderTwoDimensionalViewport
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.
inherited
debugFillProperties(DiagnosticPropertiesBuilder properties) → void
Add additional properties associated with the node.
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.
inherited
noSuchMethod(Invocation invocation) → dynamic
Invoked when a nonexistent 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 RenderTwoDimensionalViewport 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.
inherited