flutter TabBar+PageView页卡切换页面

TabController _firstPageTabController;
PageController _pageController;

class _FirstPageNewState extends State<FirstPageNew> with SingleTickerProviderStateMixin{

void initState() {
    // TODO: implement initState
    super.initState();
    _firstPageTabController = TabController(initialIndex: 0);
    _pageController = PageController(initialPage: 0);
	_firstPageTabController.addListener(_onTabChanged);
    }

 Tab 改变时，切换 PageView
_onTabChanged() {
    if (_firstPageTabController.indexIsChanging) return;
    _pageController.jumpToPage(_firstPageTabController.index);
  }
  
 // PageView 改变时，更新 TabBar
 _onPageChanged(int index) {
    if (_firstPageTabController.index != index) {
      _firstPageTabController.animateTo(index);
    }
  }

 @override
  void dispose() {
    // TODO: implement dispose
    _pageController.dispose();
    _firstPageTabController.dispose();
    super.dispose();
  }

@override
  Widget build(BuildContext context) {
    // TODO: implement build
    return DefaultTabController(
      length: pagesList.length,
      initialIndex: 0,
      child: Scaffold(
          appBar: AppBar(),
          body: _body()
      )
    );
  }

_body(){
    return PageView.builder(
        controller: _pageController,
        pageSnapping: true,
         onPageChanged: _onPageChanged,
        itemCount: pagesList.length,
        itemBuilder: (_, index){
          return PageItemView(index,key: ValueKey(index));
        });
  }

}