在flutter中如何更改FAB (浮动动作按钮)自定义动画图标

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

class MyFAB extends StatefulWidget {
  @override
  _MyFABState createState() => _MyFABState();
}

class _MyFABState extends State<MyFAB> with SingleTickerProviderStateMixin {
  AnimationController _animationController;
  Animation<double> _animation;

  @override
  void initState() {
    super.initState();
    _animationController = AnimationController(
      vsync: this,
      duration: Duration(milliseconds: 500),
    );
    _animation = Tween<double>(begin: 0, end: 1).animate(_animationController);
  }

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

  @override
  Widget build(BuildContext context) {
    return FloatingActionButton(
      onPressed: () {
        if (_animationController.isCompleted) {
          _animationController.reverse();
        } else {
          _animationController.forward();
        }
      },
      child: AnimatedIcon(
        icon: AnimatedIcons.menu_close,
        progress: _animation,
      ),
    );
  }
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(
          title: Text('Flutter FAB Animation'),
        ),
        body: Center(
          child: Text('Hello World!'),
        ),
        floatingActionButton: MyFAB(),
      ),
    );
  }
}