Page Changing with CurvedNavigationBar

import 'package:flutter/material.dart';
import 'package:curved_navigation_bar/curved_navigation_bar.dart';

void main() => runApp(MaterialApp(home: BottomNavBar()));

class BottomNavBar extends StatefulWidget {
  @override
  _BottomNavBarState createState() => _BottomNavBarState();
}

class _BottomNavBarState extends State<BottomNavBar> {
  Widget _body = Text("Body0");

  @override
  Widget build(BuildContext context) {
    return Scaffold(
        bottomNavigationBar: CurvedNavigationBar(
          initialIndex: 0,
          items: <Widget>[
            Icon(Icons.add, size: 30),
            Icon(Icons.list, size: 30),
            Icon(Icons.compare_arrows, size: 30),
            Icon(Icons.call_split, size: 30),
            Icon(Icons.perm_identity, size: 30),
          ],
          color: Colors.white,
          buttonBackgroundColor: Colors.white,
          backgroundColor: Colors.blueAccent,
          animationCurve: Curves.easeInOut,
          animationDuration: Duration(milliseconds: 600),
          onTap: (index) {
            _changeBody(index);
          },
        ),
        body: Container(
          color: Colors.blueAccent,
          child: Center(child: _body),
        ));
  }

  void _changeBody(int index) {
    switch(index){
      case 0:
        setState(() {
          _body = Text("Body0");
        });
        break;
        case 1:
        setState(() {
          _body = Text("Body1");
        });
        break;
        case 2:
        setState(() {
          _body = Text("Body2");
        });
        break;
        case 3:
        setState(() {
          _body = Text("Body3");
        });
        break;
        case 4:
        setState(() {
          _body = Text("Body4");
        });
        break;
    }
  }
}