child property Null safety
final
The widget below this widget in the tree.
The scrollbar will be stacked on top of this child. This child (and its subtree) should include a source of ScrollNotification notifications. Typically a Scrollbar is created on desktop platforms by a ScrollBehavior.buildScrollbar method, in which case the child is usually the one provided as an argument to that method.
Typically a ListView or CustomScrollView.
Implementation
final Widget child;