Scroll and update Tab bar

scroll_tab_bar.dart

import 'package:flutter/material.dart';

void main() => runApp(const MyApp());

class MyApp extends StatefulWidget {
  const MyApp({super.key});

  @override
  State<MyApp> createState() => _MyAppState();
}

class _MyAppState extends State<MyApp> {

      GlobalKey sectionOneKey = GlobalKey();
    GlobalKey sectionTwoKey = GlobalKey();
    GlobalKey sectionThreeKey = GlobalKey();


        final ScrollController _scrollController = ScrollController();

         @override
    void initState() {
      super.initState();
      _scrollController.addListener(_onScroll);
    }
int _selectedTab = 0;
        void _onScroll() {
      RenderBox renderBoxSectionOne = sectionOneKey.currentContext?.findRenderObject() as RenderBox;
            RenderBox renderBoxSectionTwo = sectionTwoKey.currentContext?.findRenderObject() as RenderBox;
            RenderBox renderBoxSectionThree = sectionThreeKey.currentContext?.findRenderObject() as RenderBox;



      Offset positionSectionOne = renderBoxSectionOne.localToGlobal(Offset.zero);
      Offset positionSectionTwo = renderBoxSectionTwo.localToGlobal(Offset.zero);
      Offset positionSectionThree = renderBoxSectionThree.localToGlobal(Offset.zero);

      // Repeat for other sections

      // Example: Check if sectionOne is visible at the top
      if (positionSectionOne.dy < MediaQuery.of(context).size.height / 2 && positionSectionOne.dy >= 0) {
        // Update selected tab to section one
        setState(() {
          _selectedTab = 0; // Assuming 0 is the index for section one
        });
      }

 if (positionSectionTwo.dy < MediaQuery.of(context).size.height / 2 && positionSectionTwo.dy >= 0) {
        // Update selected tab to section one
        setState(() {
          _selectedTab = 1; // Assuming 0 is the index for section one
        });
      }

 if (positionSectionThree.dy < MediaQuery.of(context).size.height / 2 && positionSectionThree.dy >= 0) {
        // Update selected tab to section one
        setState(() {
          _selectedTab = 2; // Assuming 0 is the index for section one
        });
      }




      // Add similar checks for other sections
    }






        @override
    void dispose() {
      _scrollController.removeListener(_onScroll);
      _scrollController.dispose();
      super.dispose();
    }
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Material App',
      home: Scaffold(
        appBar: AppBar(
          title:Row(
  spacing: 8,
  children: ['Section one', 'Section 2' , 'Section 3'].map((tab)=> 
  
  Column(
    crossAxisAlignment: .start,
    spacing: 5,
    mainAxisSize: .min,

    children: [
      IntrinsicWidth(
        child: Column(
          children: [
            Text(tab), 
             _selectedTab==['Section one', 'Section 2', 'Section 3'].indexOf(tab)?
      Divider(
        
        color:
        
        _selectedTab==['Section one', 'Section 2'].indexOf(tab)?
         Colors.amber: Colors.grey[500],
        thickness: 5,
      ):      
      Divider(
        
        color: