SliverOpacity class

A sliver widget that makes its sliver child partially transparent.

This class paints its sliver child into an intermediate buffer and then blends the sliver back into the scene partially transparent.

For values of opacity other than 0.0 and 1.0, this class is relatively expensive because it requires painting the sliver child into an intermediate buffer. For the value 0.0, the sliver child is not painted at all. For the value 1.0, the sliver child is painted immediately without an intermediate buffer.

This example shows a SliverList when the _visible member field is true, and hides it when it is false.

This is more efficient than adding and removing the sliver child widget from the tree on demand, but it does not affect how much the list scrolls (the SliverList is still present, merely invisible).


To create a local project with this code sample, run:
flutter create --sample=widgets.SliverOpacity.1 mysample

See also:

  • Opacity, which can apply a uniform alpha effect to its child using the RenderBox layout protocol.
  • AnimatedOpacity, which uses an animation internally to efficiently animate Opacity.
  • SliverVisibility, which can hide a child more efficiently (albeit less subtly, because it is either visible or hidden, rather than allowing fractional opacity values). Specifically, the SliverVisibility.maintain constructor is equivalent to using a sliver opacity widget with values of 0.0 or 1.0.


SliverOpacity({Key? key, required double opacity, bool alwaysIncludeSemantics = false, Widget? sliver})
Creates a sliver that makes its sliver child partially transparent.


alwaysIncludeSemantics bool
Whether the semantic information of the sliver child is always included.
child Widget?
The widget below this widget in the tree.
hashCode int
The hash code for this object.
no setterinherited
key Key?
Controls how one widget replaces another widget in the tree.
opacity double
The fraction to scale the sliver child's alpha value.
runtimeType Type
A representation of the runtime type of the object.
no setterinherited


createElement() SingleChildRenderObjectElement
RenderObjectWidgets always inflate to a RenderObjectElement subclass.
createRenderObject(BuildContext context) RenderSliverOpacity
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.
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.
noSuchMethod(Invocation invocation) → dynamic
Invoked when a nonexistent 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 RenderSliverOpacity 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.