“PageView tions.isNotEmpty”：在使用PageController.page生成PageView之前，无法访问它。旋转木马颤动

class MyPageView extends StatefulWidget {
  @override
  _MyPageViewState createState() => _MyPageViewState();
}

class _MyPageViewState extends State<MyPageView> {
  PageController _pageController;

  @override
  void initState() {
    super.initState();
    _pageController = PageController();
  }

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

  @override
  Widget build(BuildContext context) {
    return PageView(
      controller: _pageController,
      children: [
        // 页面1
        Container(
          color: Colors.red,
        ),
        // 页面2
        Container(
          color: Colors.blue,
        ),
        // 页面3
        Container(
          color: Colors.green,
        ),
      ],
    );
  }
}