动画 RotationTransition 如何进行指定的转数

如何进行指定的转数，例如2？正方形必须转两圈，即 360 度 * 2。在注释代码中
找到度数 = (度 * pi) / 180 ，只完成一圈，然后是完整的main.dart
代码

import 'dart:math';

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
 @override
 Widget build(BuildContext context) {
  return MaterialApp(
   debugShowCheckedModeBanner: false,
   title: 'Name App',
   theme: ThemeData(
    primarySwatch: Colors.blue,
   ),
   home: Scaffold(
    appBar: AppBar(
     title: Text('Name Page'),
    ),
    body: MyHomePage(),
   ),
  );
 }
}

class MyHomePage extends StatefulWidget {
 @override
 _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState
 extends State<MyHomePage>
 with SingleTickerProviderStateMixin {

 AnimationController _controller;
 Animation<double> _animation;

 double _width;
 double _height;
 Color _color;

 //количество оборотов
 int _turnover;

 //количество градусов
 double _degree;

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

  _width = 200.0;
  _height = 200.0;
  _color = Colors.pink;

  _turnover = 2;

  //нахождение градуса = (градус * пи) / 180
  _degree = (360 * pi) / 180;

  _controller = AnimationController(
   vsync: this,
   value: 0.0,      //default
   lowerBound: 0.0, //default
   upperBound: 1.0, //default
   duration: Duration(seconds: 1),
  );

  _animation = Tween<double>(
   begin: 0.0,
   end: _turnover * _degree //теоретически должно сделать два оборота
   )
   .animate(CurvedAnimation(parent: _controller, curve: Curves.easeInSine))
   ..addListener(() {
    setState(() {

    });
   });

  //в закоментированном коде делается только один оборот

  /*_animation = CurvedAnimation(parent: _controller, curve: Curves.easeInSine)
   ..addListener(() {
    setState(() {

    });
   });*/

 }

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

 void _f1() {
  setState(() {

  });
 }

 void _funForward() {
  setState(() {
   _controller
    ..forward();
  });
 }

 void _funReverse() {
  setState(() {
   _controller
    ..reverse();
  });
 }

 @override
 Widget build(BuildContext context) {
  return Column(
   children: <Widget>[
    Expanded(
     flex: 1,
     child: LayoutBuilder(
      builder: (context, constraints) =>
       Stack(
        children: <Widget>[
         Align(
          alignment: Alignment.center,
          child: RotationTransition(
           turns: _animation,
           child: Container(
            width: _width,
            height: _height,
            color: _color,
            alignment: Alignment.center,
            child: Text(
             '1',
             style: TextStyle(
              fontSize: 36.0,
              color: Colors.white,
             ),
            ),
           ),
          ),
         ),
        ],
       ),
     ),
    ),
    Container(
     padding: const EdgeInsets.all(8.0),
     color: Colors.orangeAccent,
     child: Row(
      children: <Widget>[
       Expanded(
        flex: 1,
        child: RaisedButton(
         onPressed: () { _funForward(); },
         splashColor: Colors.blue.withOpacity(0.5),
         shape: RoundedRectangleBorder(
          borderRadius: BorderRadius.circular(10)
         ),
         child: Text(
          'start'.toUpperCase(),
          style: TextStyle(
           color: Colors.deepPurple,
           fontSize: 16.0,
          ),
         ),
        ),
       ),
       SizedBox(width: 8.0,),
       Expanded(
        flex: 1,
        child: RaisedButton(
         onPressed: () { _funReverse(); },
         splashColor: Colors.blue.withOpacity(0.5),
         shape: RoundedRectangleBorder(
          borderRadius: BorderRadius.circular(10)
         ),
         child: Text(
          'back'.toUpperCase(),
          style: TextStyle(
           color: Colors.deepPurple,
           fontSize: 16.0,
          ),
         ),
        ),
       ),
      ],
     ),
    ),
   ],
  );
 }

}