refreshIndicatorExtent property
The amount of space the refresh indicator sliver will keep holding while onRefresh's Future is still running.
Must not be null and must be positive, but can be 0.0, in which case the sliver will start retracting back to 0.0 as soon as the refresh is started. Defaults to 60px when not specified.
Must be smaller than refreshTriggerPullDistance, since the sliver shouldn't grow further after triggering the refresh.
Implementation
final double refreshIndicatorExtent;