RenderViewport class

A render object that is bigger on the inside.

RenderViewport 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.

RenderViewport 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.

RenderViewport cannot contain RenderBox children directly. Instead, use a RenderSliverList, RenderSliverFixedExtentList, RenderSliverGrid, or a RenderSliverToBoxAdapter, for example.

See also:

Inheritance
Implemented by

Constructors

RenderViewport({AxisDirection axisDirection: AxisDirection.down, @required AxisDirection crossAxisDirection, @required ViewportOffset offset, double anchor: 0.0, List<RenderSliver> children, RenderSliver center })
Creates a viewport for RenderSliver objects. [...]

Properties

anchor double
The relative position of the zero scroll offset. [...]
read / write
center RenderSliver
The first child in the GrowthDirection.forward growth direction. [...]
read / write
childrenInHitTestOrder Iterable<RenderSliver>
Provides an iterable that walks the children of the viewport, in the order that hit-testing should use. [...]
read-only
childrenInPaintOrder Iterable<RenderSliver>
Provides an iterable that walks the children of the viewport, in the order that they should be painted. [...]
read-only
hasVisualOverflow bool
Whether the contents of this viewport would paint outside the bounds of the viewport if paint did not clip. [...]
read-only
indexOfFirstChild int
The index of the first child of the viewport relative to the center child. [...]
read-only
sizedByParent bool
Whether the constraints are the only input to the sizing algorithm (in particular, child nodes have no impact). [...]
read-only
alwaysNeedsCompositing bool
Whether this render object always needs compositing. [...]
@protected, read-only, inherited
attached bool
Whether this node is in a tree whose root is attached to something. [...]
read-only, inherited
axis Axis
The axis along which the viewport scrolls. [...]
read-only, inherited
axisDirection AxisDirection
The direction in which the SliverConstraints.scrollOffset increases. [...]
read / write, inherited
childCount int
The number of children.
read-only, inherited
constraints BoxConstraints
The box constraints most recently received from the parent.
read-only, inherited
crossAxisDirection AxisDirection
The direction in which child should be laid out in the cross axis. [...]
read / write, inherited
debugCanParentUseSize bool
Whether the parent render object is permitted to use this render object's size. [...]
read-only, inherited
debugCreator ↔ dynamic
The object responsible for creating this render object. [...]
read / write, inherited
debugDoingThisLayout bool
Whether performLayout for this render object is currently running. [...]
read-only, inherited
debugDoingThisPaint bool
Whether paint for this render object is currently running. [...]
read-only, inherited
debugDoingThisResize bool
Whether performResize for this render object is currently running. [...]
read-only, inherited
debugLayer OffsetLayer
In debug mode, the compositing layer that this render object uses to repaint. [...]
read-only, inherited
debugNeedsLayout bool
Whether this render object's layout information is dirty. [...]
read-only, inherited
debugNeedsPaint bool
Whether this render object's paint information is dirty. [...]
read-only, inherited
debugSemantics SemanticsNode
The semantics of this render object. [...]
read-only, inherited
depth int
The depth of this node in the tree. [...]
read-only, inherited
firstChild RenderSliver
The first child in the child list.
read-only, inherited
hashCode int
The hash code for this object. [...]
read-only, inherited
hasSize bool
Whether this render object has undergone layout and has a size.
read-only, inherited
isRepaintBoundary bool
Whether this render object repaints separately from its parent. [...]
read-only, inherited
lastChild RenderSliver
The last child in the child list.
read-only, inherited
layer OffsetLayer
The compositing layer that this render object uses to repaint. [...]
read-only, inherited
needsCompositing bool
Whether we or one of our descendants has a compositing layer. [...]
read-only, inherited
offset ViewportOffset
Which part of the content inside the viewport should be visible. [...]
read / write, inherited
owner PipelineOwner
The owner for this node (null if unattached). [...]
read-only, inherited
paintBounds Rect
Returns a rectangle that contains all the pixels painted by this box. [...]
read-only, inherited
parent AbstractNode
The parent of this node in the tree.
read-only, inherited
parentData ParentData
Data for use by the parent render object. [...]
read / write, inherited
runtimeType Type
A representation of the runtime type of the object.
read-only, inherited
semanticBounds Rect
The bounding box, in the local coordinate system, of this object, for accessibility purposes.
read-only, inherited
size Size
The size of this render box computed during layout. [...]
@protected, read / write, inherited

Methods

applyPaintTransform(RenderObject child, Matrix4 transform) → void
Multiply the transform from the parent's coordinate system to this box's coordinate system into the given transform. [...]
computeChildMainAxisPosition(RenderSliver child, double parentMainAxisPosition) double
Converts the parentMainAxisPosition into the child's coordinate system. [...]
debugFillProperties(DiagnosticPropertiesBuilder properties) → void
labelForChild(int index) String
A short string to identify the child with the given index. [...]
maxScrollObstructionExtentBefore(RenderSliver child) double
Returns the total scroll obstruction extent of all slivers in the viewport before child. [...]
paintOffsetOf(RenderSliver child) Offset
The offset at which the given child should be painted. [...]
performLayout() → void
performResize() → void
scrollOffsetOf(RenderSliver child, double scrollOffsetWithinChild) double
Returns the scroll offset within the viewport for the given scrollOffsetWithinChild within the given child. [...]
setupParentData(RenderObject child) → void
updateChildLayoutOffset(RenderSliver child, double layoutOffset, GrowthDirection growthDirection) → void
Called during layoutChildSequence to store the layout offset for the given child. [...]
updateOutOfBandData(GrowthDirection growthDirection, SliverGeometry childLayoutGeometry) → void
Called during layoutChildSequence for each child. [...]
add(RenderSliver child) → void
Append child to the end of this render object's child list.
inherited
addAll(List<RenderSliver> children) → void
Add all the children to the end of this render object's child list.
inherited
adoptChild(RenderObject child) → void
Called by subclasses when they decide a render object is a child. [...]
inherited
assembleSemanticsNode(SemanticsNode node, SemanticsConfiguration config, Iterable<SemanticsNode> children) → void
Assemble the SemanticsNode for this RenderObject. [...]
inherited
attach(PipelineOwner owner) → void
inherited
childAfter(RenderSliver child) RenderSliver
The next child after the given child in the child list.
inherited
childBefore(RenderSliver child) RenderSliver
The previous child before the given child in the child list.
inherited
clearSemantics() → void
Removes all semantics from this render object and its descendants. [...]
@mustCallSuper, inherited
computeAbsolutePaintOffset(RenderSliver child, double layoutOffset, GrowthDirection growthDirection) Offset
The offset at which the given child should be painted. [...]
@protected, inherited
computeDistanceToActualBaseline(TextBaseline baseline) double
Returns the distance from the y-coordinate of the position of the box to the y-coordinate of the first given baseline in the box's contents, if any, or null otherwise. [...]
@protected, inherited
computeMaxIntrinsicHeight(double width) double
Computes the value returned by getMaxIntrinsicHeight. Do not call this function directly, instead, call getMaxIntrinsicHeight. [...]
inherited
computeMaxIntrinsicWidth(double height) double
Computes the value returned by getMaxIntrinsicWidth. Do not call this function directly, instead, call getMaxIntrinsicWidth. [...]
inherited
computeMinIntrinsicHeight(double width) double
Computes the value returned by getMinIntrinsicHeight. Do not call this function directly, instead, call getMinIntrinsicHeight. [...]
inherited
computeMinIntrinsicWidth(double height) double
Computes the value returned by getMinIntrinsicWidth. Do not call this function directly, instead, call getMinIntrinsicWidth. [...]
inherited
debugAdoptSize(Size value) Size
Claims ownership of the given Size. [...]
inherited
debugAssertDoesMeetConstraints() → void
Verify that the object's constraints are being met. Override this function in a subclass to verify that your state matches the constraints object. This function is only called in checked mode and only when needsLayout is false. If the constraints are not met, it should assert or throw an exception.
inherited
debugDescribeChildren() List<DiagnosticsNode>
inherited
debugHandleEvent(PointerEvent event, HitTestEntry entry) bool
Implements the debugPaintPointersEnabled debugging feature. [...]
inherited
debugPaint(PaintingContext context, Offset offset) → void
Override this method to paint debugging information.
inherited
debugPaintBaselines(PaintingContext context, Offset offset) → void
In debug mode, paints a line for each baseline. [...]
@protected, inherited
debugPaintPointers(PaintingContext context, Offset offset) → void
In debug mode, paints a rectangle if this render box has counted more pointer downs than pointer up events. [...]
@protected, inherited
debugPaintSize(PaintingContext context, Offset offset) → void
In debug mode, paints a border around this render box. [...]
inherited
debugRegisterRepaintBoundaryPaint({bool includedParent: true, bool includedChild: false }) → void
Called, in checked mode, if isRepaintBoundary is true, when either the this render object or its parent attempt to paint. [...]
inherited
debugResetSize() → void
If a subclass has a "size" (the state controlled by parentUsesSize, whatever it is in the subclass, e.g. the actual size property of RenderBox), and the subclass verifies that in checked mode this "size" property isn't used when debugCanParentUseSize isn't set, then that subclass should override debugResetSize to reapply the current values of debugCanParentUseSize to that state.
inherited
debugThrowIfNotCheckingIntrinsics() bool
Throws an exception saying that the object does not support returning intrinsic dimensions if, in checked mode, we are not in the RenderObject.debugCheckingIntrinsics mode. [...]
@protected, inherited
debugValidateChild(RenderObject child) bool
Checks whether the given render object has the correct runtimeType to be a child of this render object. [...]
inherited
describeApproximatePaintClip(RenderObject child) Rect
Returns a rect in this object's coordinate system that describes the approximate bounding box of the clip rect that would be applied to the given child during the paint phase, if any. [...]
inherited
describeSemanticsConfiguration(SemanticsConfiguration config) → void
Report the semantics of this node, for example for accessibility purposes. [...]
inherited
detach() → void
inherited
dropChild(RenderObject child) → void
Called by subclasses when they decide a render object is no longer a child. [...]
inherited
getDistanceToActualBaseline(TextBaseline baseline) double
Calls computeDistanceToActualBaseline and caches the result. [...]
@mustCallSuper, @protected, inherited
getDistanceToBaseline(TextBaseline baseline, { bool onlyReal: false }) double
Returns the distance from the y-coordinate of the position of the box to the y-coordinate of the first given baseline in the box's contents. [...]
inherited
getMaxIntrinsicHeight(double width) double
Returns the smallest height beyond which increasing the height never decreases the preferred width. The preferred width is the value that would be returned by getMinIntrinsicWidth for that height. [...]
@mustCallSuper, inherited
getMaxIntrinsicWidth(double height) double
Returns the smallest width beyond which increasing the width never decreases the preferred height. The preferred height is the value that would be returned by getMinIntrinsicHeight for that width. [...]
@mustCallSuper, inherited
getMinIntrinsicHeight(double width) double
Returns the minimum height that this box could be without failing to correctly paint its contents within itself, without clipping. [...]
@mustCallSuper, inherited
getMinIntrinsicWidth(double height) double
Returns the minimum width that this box could be without failing to correctly paint its contents within itself, without clipping. [...]
@mustCallSuper, inherited
getOffsetToReveal(RenderObject target, double alignment) double
Returns the offset that would be needed to reveal the target render object. [...]
inherited
getTransformTo(RenderObject ancestor) Matrix4
Applies the paint transform up the tree to ancestor. [...]
inherited
globalToLocal(Offset point, { RenderObject ancestor }) Offset
Convert the given point from the global coordinate system in logical pixels to the local coordinate system for this box. [...]
inherited
handleEvent(PointerEvent event, HitTestEntry entry) → void
Override this method to handle pointer events that hit this render object. [...]
inherited
hitTest(HitTestResult result, { Offset position }) bool
Determines the set of render objects located at the given position. [...]
inherited
hitTestChildren(HitTestResult result, { Offset position }) bool
Override this method to check whether any children are located at the given position. [...]
inherited
hitTestSelf(Offset position) bool
Override this method if this render object can be hit even if its children were not hit. [...]
@protected, inherited
insert(RenderSliver child, { RenderSliver after }) → void
Insert child into this render object's child list after the given child. [...]
inherited
invokeLayoutCallback<T extends Constraints>(LayoutCallback<T> callback) → void
Allows mutations to be made to this object's child list (and any descendants) as well as to any other dirty nodes in the render tree owned by the same PipelineOwner as this object. The callback argument is invoked synchronously, and the mutations are allowed only during that callback's execution. [...]
@protected, inherited
layout(Constraints constraints, { bool parentUsesSize: false }) → void
Compute the layout for this render object. [...]
inherited
layoutChildSequence(RenderSliver child, double scrollOffset, double overlap, double layoutOffset, double remainingPaintExtent, double mainAxisExtent, double crossAxisExtent, GrowthDirection growthDirection, RenderSliver advance(RenderSliver child)) double
Determines the size and position of some of the children of the viewport. [...]
@protected, inherited
localToGlobal(Offset point, { RenderObject ancestor }) Offset
Convert the given point from the local coordinate system for this box to the global coordinate system in logical pixels. [...]
inherited
markNeedsCompositingBitsUpdate() → void
Mark the compositing state for this render object as dirty. [...]
inherited
markNeedsLayout() → void
Mark this render object's layout information as dirty, and either register this object with its PipelineOwner, or defer to the parent, depending on whether this object is a relayout boundary or not respectively. [...]
inherited
markNeedsLayoutForSizedByParentChange() → void
Mark this render object's layout information as dirty (like markNeedsLayout), and additionally also handle any necessary work to handle the case where sizedByParent has changed value. [...]
inherited
markNeedsPaint() → void
Mark this render object as having changed its visual appearance. [...]
inherited
markNeedsSemanticsUpdate() → void
Mark this node as needing an update to its semantics description. [...]
inherited
markParentNeedsLayout() → void
Mark this render object's layout information as dirty, and then defer to the parent. [...]
@protected, inherited
move(RenderSliver child, { RenderSliver after }) → void
Move this child in the child list to be before the given child. [...]
inherited
noSuchMethod(Invocation invocation) → dynamic
Invoked when a non-existent method or property is accessed. [...]
inherited
paint(PaintingContext context, Offset offset) → void
Paint this render object into the given context at the given offset. [...]
inherited
reassemble() → void
Cause the entire subtree rooted at the given RenderObject to be marked dirty for layout, paint, etc, so that the effects of a hot reload can be seen, or so that the effect of changing a global debug flag (such as debugPaintSizeEnabled) can be applied. [...]
inherited
redepthChild(AbstractNode child) → void
Adjust the depth of the given child to be greater than this node's own depth. [...]
@protected, inherited
redepthChildren() → void
Adjust the depth of this node's children, if any. [...]
inherited
remove(RenderSliver child) → void
Remove this child from the child list. [...]
inherited
removeAll() → void
Remove all their children from this render object's child list. [...]
inherited
replaceRootLayer(OffsetLayer rootLayer) → void
Replace the layer. This is only valid for the root of a render object subtree (whatever object scheduleInitialPaint was called on). [...]
inherited
rotate({int oldAngle, int newAngle, Duration time }) → void
Rotate this render object (not yet implemented).
inherited
scheduleInitialLayout() → void
Bootstrap the rendering pipeline by scheduling the very first layout. [...]
inherited
scheduleInitialPaint(ContainerLayer rootLayer) → void
Bootstrap the rendering pipeline by scheduling the very first paint. [...]
inherited
scheduleInitialSemantics() → void
Bootstrap the semantics reporting mechanism by marking this node as needing a semantics update. [...]
inherited
showOnScreen([RenderObject child ]) → void
Attempt to make this or a descendant RenderObject visible on screen. [...]
inherited
toDiagnosticsNode({String name, DiagnosticsTreeStyle style }) DiagnosticsNode
inherited
toString({DiagnosticLevel minLevel }) String
inherited
toStringDeep({String prefixLineOne: '', String prefixOtherLines: '', DiagnosticLevel minLevel: DiagnosticLevel.debug }) String
Returns a description of the tree rooted at this node. If the prefix argument is provided, then every line in the output will be prefixed by that string.
inherited
toStringShallow({String joiner: '; ', DiagnosticLevel minLevel: DiagnosticLevel.debug }) String
Returns a one-line detailed description of the render object. This description is often somewhat long. [...]
inherited
toStringShort() String
Returns a human understandable name.
inherited
visitChildren(RenderObjectVisitor visitor) → void
Calls visitor for each immediate child of this render object. [...]
inherited
visitChildrenForSemantics(RenderObjectVisitor visitor) → void
Called when collecting the semantics of this node. [...]
inherited

Operators

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

Constants

excludeFromScrolling → const SemanticsTag
When a top-level SemanticsNode below a RenderAbstractViewport is tagged with excludeFromScrolling it will not be part of the scrolling area for semantic purposes. [...]
const SemanticsTag('RenderViewport.excludeFromScrolling')
useTwoPaneSemantics → const SemanticsTag
If a RenderAbstractViewport overrides RenderObject.describeSemanticsConfiguration to add the SemanticsTag useTwoPaneSemantics to its SemanticsConfiguration, two semantics nodes will be used to represent the viewport with its associated scrolling actions in the semantics tree. [...]
const SemanticsTag('RenderViewport.twoPane')