动画之间发生错误

做了错误消息中写的内容：替换Tween<Color>为ColorTween. 我也用 替换了所有的刘海，late但这不再重要。

import 'package:flutter/material.dart';

void main() => runApp(const MyApp());

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

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      debugShowCheckedModeBanner: false,
      title: 'Name App',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: const MyHomePage(),
    );
  }
}

class MyHomePage extends StatefulWidget {
  const MyHomePage({Key? key}) : super(key: key);

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> with SingleTickerProviderStateMixin {
  String _str = '1';
  bool _b = false;

  late Curve _curve;
  late AnimationController _animationController;
  late Animation<Color?> _animateColor;
  late Animation<double> _animateIcon;

  @override
  void initState() {
    super.initState();

    _curve = Curves.easeOut;

    _animationController =
        AnimationController(vsync: this, duration: const Duration(milliseconds: 500))
          ..addListener(() {
            setState(() {});
          });

    _animateColor = ColorTween(
      begin: Colors.green,
      end: Colors.lightBlue,
    ).animate(CurvedAnimation(
      parent: _animationController,
      curve: Interval(0.00, 1.00, curve: _curve),
    ));

    _animateIcon = Tween<double>(begin: 0.0, end: 1.0).animate(_animationController);
  }

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

  void _f1() {
    setState(() {
      if (_b) {
        _str = '1';
        _b = false;
        _animationController.reverse();
      } else {
        _str = '2';
        _b = true;
        _animationController.forward();
      }
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text('Name Page'),
      ),
      body: SafeArea(
        child: Center(
          child: Text(
            _str,
            style: const TextStyle(fontSize: 36.0, color: Colors.pink),
          ),
        ),
      ),

      //кнопка
      floatingActionButton: FloatingActionButton(
        onPressed: () {
          _f1();
        },
        child: AnimatedIcon(
          icon: AnimatedIcons.menu_close,
          progress: _animateIcon,
        ),
        backgroundColor: _animateColor.value,
        foregroundColor: Colors.white,
      ),

      //расположение кнопки
      floatingActionButtonLocation: FloatingActionButtonLocation.centerDocked,

      //бар находится только внизу
      bottomNavigationBar: BottomAppBar(
        child: Container(
          height: 50.0,
        ),
        color: Colors.amber,
        shape: const CircularNotchedRectangle(),
        notchMargin: 8.0,
      ),
    );
  }
}