如何在用户点击BottomNavigationBarItem时显示颤动modalBottomSheet

import 'package:flutter/material.dart';

class MyPage extends StatefulWidget {
  @override
  _MyPageState createState() => _MyPageState();
}

class _MyPageState extends State<MyPage> with SingleTickerProviderStateMixin {
  AnimationController _controller;
  Animation<double> _animation;

  @override
  void initState() {
    super.initState();
    _controller = AnimationController(
      duration: const Duration(milliseconds: 500),
      vsync: this,
    );
    _animation = Tween(begin: 0.0, end: 1.0).animate(
      CurvedAnimation(
        parent: _controller,
        curve: Curves.easeInOut,
      ),
    );
  }

  @override
  void dispose() {
    _controller.dispose();
    super.dispose();
  }

  void _showModalBottomSheet() {
    showModalBottomSheet(
      context: context,
      builder: (BuildContext context) {
        return AnimatedBuilder(
          animation: _animation,
          builder: (BuildContext context, Widget child) {
            return Transform.scale(
              scale: _animation.value,
              child: Container(
                height: 200.0,
                child: Center(
                  child: Text(
                    'Modal Bottom Sheet',
                    style: TextStyle(fontSize: 24.0),
                  ),
                ),
              ),
            );
          },
        );
      },
    );
    _controller.forward(from: 0.0);
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Flutter App'),
      ),
      body: Center(
        child: Text(
          'Click BottomNavigationBarItem to show modalBottomSheet',
          style: TextStyle(fontSize: 18.0),
        ),
      ),
      bottomNavigationBar: BottomNavigationBar(
        items: [
          BottomNavigationBarItem(
            icon: Icon(Icons.home),
            label: 'Home',
          ),
          BottomNavigationBarItem(
            icon: Icon(Icons.settings),
            label: 'Settings',
          ),
        ],
        onTap: (index) {
          if (index == 1) {
            _showModalBottomSheet();
          }
        },
      ),
    );
  }
}

void main() {
  runApp(MaterialApp(
    home: MyPage(),
  ));
}