我正在使用一个名为bubble_bottom_bar1.2.0的flutter底部导航，它工作得很好，但是当我单击选项卡时什么也不做，当我单击导航栏时如何改变屏幕？ 下面是我的代码:

import 'package:flutter/material.dart';
import 'package:wallet_app/CardScreen.dart';
import 'package:wallet_app/HomeScreen.dart';
import 'package:bubble_bottom_bar/bubble_bottom_bar.dart';

import 'package:cloud_firestore/cloud_firestore.dart';
void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        // This is the theme of your application.
        //
        // Try running your application with "flutter run". You'll see the
        // application has a blue toolbar. Then, without quitting the app, try
        // changing the primarySwatch below to Colors.green and then invoke
        // "hot reload" (press "r" in the console where you ran "flutter run",
        // or simply save your changes to "hot reload" in a Flutter IDE).
        // Notice that the counter didn't reset back to zero; the application
        // is not restarted.
        primarySwatch: Colors.blue,
      ),
      home: WalletApp(),
      debugShowCheckedModeBanner: false,
    );
  }
}

class WalletApp extends StatefulWidget {
  @override
    final databaseReference = Firestore.instance;

  _WalletAppState createState() => _WalletAppState();
}

class _WalletAppState extends State<WalletApp> {
    int currentIndex;
  @override
  void initState() {
    // TODO: implement initState
    super.initState();
    currentIndex = 0;
  }

  void changePage(int index) {
    setState(() {
      currentIndex = index;
    });
  }
  var screens = [
    HomeScreen(),
    CardScreen(),
  ]; //screens for each tab

  int selectedTab = 0;
    GlobalKey<ScaffoldState> _drawerKey = GlobalKey();


  @override
  Widget build(BuildContext context) {
    return Scaffold(
      backgroundColor: Color.fromRGBO(38, 81, 158, 1),key: _drawerKey,
    appBar: AppBar(
    backgroundColor: Colors.transparent,
    elevation: 0.0,
    iconTheme: new IconThemeData(color: Colors.black),
   
)//,floatingActionButton: FloatingActionButton(
   //     onPressed: () {},
     //   child: Icon(Icons.add),
       // backgroundColor: Colors.blueAccent,
      //),
      //floatingActionButtonLocation: FloatingActionButtonLocation.startFloat,
      ,bottomNavigationBar: BubbleBottomBar(
        hasNotch: true,
        fabLocation: BubbleBottomBarFabLocation.end,
        opacity: .2,
        currentIndex: currentIndex,
        onTap: changePage,
        borderRadius: BorderRadius.vertical(
            top: Radius.circular(
                16)), //border radius doesn't work when the notch is enabled.
        elevation: 8,
        items: <BubbleBottomBarItem>[
          BubbleBottomBarItem(
              backgroundColor: Colors.blueAccent,
              icon: Icon(
                Icons.home,
                color: Colors.black,
              ),
              activeIcon: Icon(
                Icons.home,
                color: Colors.white,
              ),
              title: Text("Home")),
          BubbleBottomBarItem(
              backgroundColor: Colors.deepPurple,
              icon: Icon(
                Icons.access_time,
                color: Colors.black,
              ),
              activeIcon: Icon(
                Icons.access_time,
                color: Colors.deepPurple,
              ),
              title: Text("Logs")),
          BubbleBottomBarItem(
              backgroundColor: Colors.indigo,
              icon: Icon(
                Icons.folder_open,
                color: Colors.black,
              ),
              activeIcon: Icon(
                Icons.folder_open,
                color: Colors.indigo,
              ),
              title: Text("Folders")),
          BubbleBottomBarItem(
              backgroundColor: Colors.green,
              icon: Icon(
                Icons.menu,
                color: Colors.black,
              ),
              activeIcon: Icon(
                Icons.menu,
                color: Colors.green,
              ),
              title: Text("Menu"))
        ],
      ),
 
     
    
      body: screens[selectedTab],
    );
  }
}