maintainSize property
Whether to maintain space for where the sliver would have been.
To set this, maintainAnimation must also be set.
Maintaining the size when the sliver is not visible is not notably more
expensive than just keeping animations running without maintaining the
size, and may in some circumstances be slightly cheaper if the subtree is
simple and the visible property is frequently toggled, since it avoids
triggering a layout change when the visible property is toggled. If the
sliver subtree is not trivial then it is significantly cheaper to not
even keep the state (see maintainState).
If this property is true, SliverOpacity is used instead of SliverOffstage.
If this property is false, then maintainSemantics and maintainInteractivity must also be false.
Dynamically changing this value may cause the current state of the subtree to be lost (and a new instance of the subtree, with new State objects, to be immediately created if visible is true).
Implementation
final bool maintainSize;