[Flutter] `vsync` property in TabController constructor

According to this: sample code

I created my own implementation of TabController:

void main() {
runApp(new MyApp());
}

class MyApp extends StatefulWidget {

@override
_MyAppState createState() => new _MyAppState();
}

class _MyAppState extends State<MyApp> {

TabController _tabController;

@override
void initState() {
super.initState();
_tabController = new TabController(vsync: this, length: choices.length);
}

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

@override
Widget build(BuildContext context) {
return new MaterialApp(
home: new Scaffold(
bottomNavigationBar: new Material(
color: Colors.blue,
child: new TabBar(
controller: _tabController,
isScrollable: false,
tabs: choices.map((Choice choice) {
return new Tab(
text: null,
icon: new Icon(choice.icon),
);
}).toList(),
),
),
appBar: new AppBar(
title: const Text('Swap'),
),
body: new TabBarView(
controller: _tabController,
children: choices.map((Choice choice) {
return new Padding(
padding: const EdgeInsets.all(16.0),
child: new ChoiceCard(choice: choice),
);
}).toList(),
),
),
);
}
}


In line: _tabController = new TabController(vsync: this, length: choices.length); I got error this message:

error: The argument type '_MyAppState' can't be assigned to the parameter type 'TickerProvider'. (argument_type_not_assignable at [swap] lib/main.dart:24)
​

What is wrong with my code?

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