child property Null safety
The widget below this widget in the tree.
The overscroll indicator will apply a stretch effect to this child. This child (and its subtree) should include a source of ScrollNotification notifications.
Typically a StretchingOverscrollIndicator is created by a ScrollBehavior.buildOverscrollIndicator method when opted-in using the ScrollBehavior.androidOverscrollIndicator flag. In this case the child is usually the one provided as an argument to that method. ScrollBehavior.androidOverscrollIndicator is deprecated, use ThemeData.useMaterial3, or override ScrollBehavior.buildOverscrollIndicator to choose the desired indicator.
final Widget? child;