create scrollcontroller

create_scrollcontroller.dart

final _scrollController = ScrollController();

@override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
        child: ListView.builder(
          // assign scroll controller to list view
          controller: _scrollController,
          itemBuilder: (context, index) {
            return ListTile(
              // assign key to each item
              key: _fruitKeys[index],
              title: Text(fruits[index]),
            );
          },
          itemCount: fruits.length,
        ),
      ),
      floatingActionButton: FloatingActionButton.extended(
        tooltip: 'Scroll to Mandarina',
        onPressed: _scrollToWidget,
        label: const Text('Scroll to Mandarina'),
        icon: const Icon(Icons.arrow_upward_rounded),
      ),
    );
  }