复制步骤：向左滑动，切换到红色Tab，然后再次切换到紫色Tab。
什么是：执行步骤后再现，第一个Tab的PageView再次在蓝页。
应该是：在执行步骤以再现之后，第一个Tab的PageView仍然在绿色页。
我错过了什么？

import "package:flutter/material.dart";
import "package:flutter/services.dart";

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

class MyApp extends StatelessWidget {
  @override
    Widget build(BuildContext context) {
      SystemChrome.setEnabledSystemUIOverlays([]);
      return MaterialApp(
        home: MyHome()
      );
    }
}

class MyHomeState extends State<MyHome> with TickerProviderStateMixin {
  TabController tabController;
  @override
    void initState() {
      tabController = tabController?? TabController(
        vsync: this,
        length: 2
      );
      super.initState();
    }
  @override
    void dispose() {
      tabController.dispose();
      super.dispose();
    }
  @override
    Widget build(BuildContext context) {
      return Scaffold(
        body: Column(
          children: [
            TabBar(
              controller: tabController,
              tabs: [
                Container(
                  color: Colors.purple,
                  width: 100.0,
                  height: 50.0
                ),
                Container(
                  color: Colors.pink,
                  width: 100.0,
                  height: 50.0
                )
              ]
            ),
            Expanded(
              child: TabBarView(
                controller: tabController,
                children: [
                  MyPageView(),
                  MyPageView(),
                ],
              )
            )
          ]
        )
      );
    }
}
class MyHome extends StatefulWidget {
  @override
    State<StatefulWidget> createState() {
      return MyHomeState();
    }
}

class MyPageViewState extends State<MyPageView> {
  PageController pageController;
  @override
    void initState() {
      pageController = pageController?? PageController();
      super.initState();
    }
    @override
      void dispose() {
        pageController.dispose();
        super.dispose();
      }
  @override
    Widget build(BuildContext context) {
      return PageView(
        controller: pageController,
        children: [
          Container(
            color: Colors.blue
          ),
          Container(
            color: Colors.green
          )
        ]
      );
    }
}
class MyPageView extends StatefulWidget {
  @override
    State<StatefulWidget> createState() {
      return MyPageViewState();
    }
}