flutter - How to know if a widget is visible within a viewport?

Question

I have a view that consists of a Scaffold and a single ListView in its body, each children of the list is a different widget that represents various "sections" of the view (sections range from simple TextViews to arrangements of Columns and Rows), I want to show a FloatingActionButon only when the user scrolls over certain Widgets (which aren't initially visible due to being far down the list).

Answer 1

https://pub.dev/packages/visibility_detector provides this functionality with its VisibilityDetector widget that can wrap any other Widget and notify when the visible area of the widget changed:

VisibilityDetector(
   key: Key("unique key"),
   onVisibilityChanged: (VisibilityInfo info) {
       debugPrint("${info.visibleFraction} of my widget is visible");
   },
   child: MyWidgetToTrack());
)