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).

link

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.
Inheritance

Constructors

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

Properties

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

Methods

createElement() → SingleChildRenderObjectElement
RenderObjectWidgets always inflate to a RenderObjectElement subclass.
inherited
createRenderObject(BuildContext context) → RenderSliverOpacity
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.
override
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 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.
override

Operators

operator ==(Object other) → bool
The equality operator.
inherited