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 simply 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:
bool _visible = true;
List<Widget> listItems = <Widget>[
  Text('Now you see me,'),
  Text('Now you don\'t!'),
];

SliverOpacity(
  opacity: _visible ? 1.0 : 0.0,
  sliver: SliverList(
    delegate: SliverChildListDelegate(listItems),
  ),
)

This is more efficient than adding and removing the sliver child widget from the tree on demand.

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.
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
opacity double
The fraction to scale the sliver child's alpha value. [...]
final
child Widget
The widget 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

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