A Working BottomNavigationBar (Just use it on main.dart)

main_dashboard.dart

import 'package:flutter/cupertino.dart';
import 'package:flutter/material.dart';
import 'package:get/get_state_manager/src/simple/get_controllers.dart';
import 'package:get/get_state_manager/src/simple/get_state.dart';
import 'package:rilmit_streamit/feed_screen/feed_mainScreen.dart';

class MainDashboard extends StatefulWidget {
  @override
  _MainDashboardState createState() => _MainDashboardState();
}
class _MainDashboardState extends State<MainDashboard> {
  int _selectedIndex = 0;
  final PageController _pageController = PageController();

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: PageView(
        controller: _pageController,
        children: const <Widget>[
          Scaffold(),
          FeedMainScreen(),
        ],
        // physics: const NeverScrollableScrollPhysics(), // disable swipe
        onPageChanged: (pageIndex) { // On Swipe left or right
          setState(() => _selectedIndex = pageIndex);
        },
      ),
      bottomNavigationBar: BottomNavigationBar(
        selectedItemColor: Colors.orange,
        currentIndex: _selectedIndex,
        onTap: (value) { // onTap Bottom icon
          setState(() => _selectedIndex = value);
          _pageController.jumpToPage(value);
        },
        items: [
          BottomNavigationBarItem(
              icon: Icon(Icons.chat), title: Text('Shop')),
          BottomNavigationBarItem(
              icon: Icon(Icons.home), title: Text('Home')),

        ],
      ),
    );
  }
}

main_dashboard_basedGetx.dart

import 'package:flutter/cupertino.dart';
import 'package:flutter/material.dart';
import 'package:get/get_core/src/get_main.dart';
import 'package:get/get_state_manager/src/simple/get_controllers.dart';
import 'package:get/get_instance/src/extension_instance.dart';
import 'package:get/get_state_manager/src/simple/get_state.dart';

import 'feed_screen/feed_mainScreen.dart';


class DashboardController extends GetxController{
  int selectedIndex = 0;
  PageController pageController = PageController();

  void changeIndex(value){
    selectedIndex = value;
    // To notify GetBuilder
    update();
  }
}

class MainDashboardNew extends StatelessWidget {
  MainDashboardNew({Key? key}) : super(key: key);

  final DashboardController dashboardController = Get.put(DashboardController());

  @override
  Widget build(BuildContext context) {

    return GetBuilder<DashboardController>(
        builder: (_) {

          PageController _pageController = dashboardController.pageController;
          int _selectedIndex = dashboardController.selectedIndex;
        return Scaffold(
          body: PageView(
            controller: _pageController,
            children: const <Widget>[
              Scaffold(backgroundColor: Colors.green,),
              FeedMainScreen(),
            ],
            // physics: const NeverScrollableScrollPhysics(), // disable swipe
            onPageChanged: (pageIndex) { // On Swipe left or right
              dashboardController.changeIndex(pageIndex);
            },
          ),
          bottomNavigationBar: BottomNavigationBar(
            selectedItemColor: Colors.orange,
            currentIndex: _selectedIndex,
            onTap: (value) { // onTap Bottom icon
              dashboardController.changeIndex(value);
              _pageController.jumpToPage(value);
            },
            items: const [
              BottomNavigationBarItem(
                  icon: Icon(Icons.chat), title: Text('Shop')),
              BottomNavigationBarItem(
                  icon: Icon(Icons.home), title: Text('Home')),
            ],
          ),
        );
      }
    );
  }
}