SliverAnimatedOpacity class

Animated version of SliverOpacity which automatically transitions the sliver child's opacity over a given duration whenever the given opacity changes.

Animating an opacity is relatively expensive because it requires painting the sliver child into an intermediate buffer.

Here's an illustration of what using this widget looks like, using a curve of Curves.fastOutSlowIn.

Hit testing

Setting the opacity to zero does not prevent hit testing from being applied to the descendants of the SliverAnimatedOpacity widget. This can be confusing for the user, who may not see anything, and may believe the area of the interface where the SliverAnimatedOpacity is hiding a widget to be non-interactive.

With certain widgets, such as Flow, that compute their positions only when they are painted, this can actually lead to bugs (from unexpected geometry to exceptions), because those widgets are not painted by the SliverAnimatedOpacity widget at all when the opacity animation reaches zero.

To avoid such problems, it is generally a good idea to use a SliverIgnorePointer widget when setting the opacity to zero. This prevents interactions with any children in the subtree when the sliver is animating away.

See also:

• SliverFadeTransition, an explicitly animated version of this widget, where an Animation is provided by the caller instead of being built in.
• AnimatedOpacity, for automatically transitioning a box child's opacity over a given duration whenever the given opacity changes.