getting error No TabController for TabBar. but after few seconds data is visible.

[jhon]

i have tried this

class Homepage extends StatefulWidget {

  _HomepageState createState() => _HomepageState();

}

class _HomepageState extends State<Homepage>

    with SingleTickerProviderStateMixin {

  TabController _tabController;

  List<Tab> tabs = [];

  int tabCount = 0;

  final CollectionReference categoryCollection =

      FirebaseFirestore.instance.collection('categories');

  @override

  void initState() {

    super.initState();

    categoryTabs();

  }

  @override

  void dispose() {

    _tabController.dispose();

    super.dispose();

  }

  void tabSelection() {

    setState(() {});

  }

  Future<void> categoryTabs() async {

    await categoryCollection.get().then((QuerySnapshot snapshot) {

      if (snapshot.docs.isNotEmpty) {

        List<Tab> _tabs = [];

        for (int i = 0; i < snapshot.docs.length; i++) {

          DocumentSnapshot snap = snapshot.docs[i];

          // tabCount++;

          _tabs.add(

            Tab(

              child: Text(snap.get("docid")),

            ),

          );

        }

        setState(() {

          tabCount = _tabs.length;

          tabs = _tabs;

          _tabController = TabController(vsync: this, length: tabCount);

          _tabController.addListener(tabSelection);

        });

      }

    });

  }

  @override

  Widget build(BuildContext context) {

    return Scaffold(

      appBar: AppBar(

          bottom: TabBar(

              controller: _tabController,

              isScrollable: true,

              indicatorPadding: EdgeInsets.all(0.0),

              tabs: tabs)),

      body: TabBarView(

        controller: _tabController,

        children: <Widget>[

          Text("test"),

          Text("test"),

          Text("test"),

        ],

      ),

    );

  }

}