我如何为导航栏按钮之一提供索引？

Question

我是flutter新手，谁能指导我如何在导航栏（）中调用长度或索引

import 'package:flutter/material.dart';

class MENU extends StatefulWidget {

  const MENU({Key? key}) : super(key: key);

  @override
  State<MENU> createState() => _MENUState();
}

class _MENUState extends State<MENU> {

  var pages = [Favourites(items: CatalogModel.items.length), MainMenu(), Profile()];
  int _selectedIndex = 0;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: pages[_selectedIndex],
      // BOTTOM NAVIGATION BAR
      bottomNavigationBar: BottomNavigationBar(
        backgroundColor: Color(0xFFF3E5F5),
        elevation: 0,
        items: [
          BottomNavigationBarItem(
              icon: Icon(Icons.favorite_outline_sharp), label: "Specialities"),
          BottomNavigationBarItem(icon: Icon(Icons.list), label: "Menu"),
          BottomNavigationBarItem(icon: Icon(Icons.person), label: "Profile"),
        ],
        currentIndex: _selectedIndex,
        // selectedItemColor: Colors.amber[800],
        onTap: (setValue) {
          setState(() {
            _selectedIndex = setValue;
          });
        },
      ),
      floatingActionButton: FloatingActionButton.small(
        onPressed: () {
          Navigator.push(
              context, MaterialPageRoute(builder: (context) => CART()));
        },
        child: Icon(
          CupertinoIcons.cart_badge_plus,
          size: 25,
        ),
      ),
      floatingActionButtonLocation: FloatingActionButtonLocation.endDocked,
    );
  }
}

我试图为 CatalogModel.items.index 提供索引，但它显示错误