getThumbScrollOffset method
The thumb's corresponding scroll offset in the track.
Implementation
double getThumbScrollOffset() {
final double scrollableExtent =
_lastMetrics!.maxScrollExtent - _lastMetrics!.minScrollExtent;
final double fractionPast = (scrollableExtent > 0)
? clampDouble(_lastMetrics!.pixels / scrollableExtent, 0.0, 1.0)
: 0;
return fractionPast * (_traversableTrackExtent - _thumbExtent);
}