Flutter delayed function called twice

Question

I have a launcher screen where I check do I have specific data or not. Depending on the result I show different screens

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


 class MyApp extends StatelessWidget {
   @override
    Widget build(BuildContext context) {
    return MaterialApp(
    theme: ThemeData(
      primarySwatch: Colors.blue,
    ),
    home: LauncherScreen()
  );
 }
}


 class LauncherScreen extends StatelessWidget {
 @override
 Widget build(BuildContext context) {
 print("build, build");
 Future.delayed(new Duration(milliseconds: 2000), () {
  LocalData localData = LocalData();
  localData.getCity().then((city) {
    if (city != null) {
      Const.city = city;
      Navigator.push(
        context,
        MaterialPageRoute(builder: (context) => Home()),
      );
    } else {
      Navigator.push(
        context,
        MaterialPageRoute(builder: (context) => SelectCities()),
      );
    }
  });
});
return Container(
    width: double.infinity,
    height: double.infinity,
     color: Color(GoEngColors.violet));
 }
}

My LauncherScreen called twice and as a result, I see my Home or Select city screen appears twice.

What is the reason of such behaviour and how to solve it? Thanks.

Answer 1

The build method can be called multiple times, so it's not the right place to call initialization processes. You should convert your widget to StatefulWidget (Alt + Enter on Android Studio) and call your Future.delayed from initState(). Like this:

class LauncherScreen extends StatefulWidget {
  @override
  _LauncherScreenState createState() => _LauncherScreenState();
}

class _LauncherScreenState extends State<LauncherScreen> {

  @override
  void initState() {
    super.initState();
    print("build, build");
    Future.delayed(new Duration(milliseconds: 2000), () {
      LocalData localData = LocalData();
      localData.getCity().then((city) {
        if (city != null) {
          Const.city = city;
          Navigator.push(
            context,
            MaterialPageRoute(builder: (context) => Home()),
          );
        } else {
          Navigator.push(
            context,
            MaterialPageRoute(builder: (context) => SelectCities()),
          );
        }
      });
    });
  }

  @override
  Widget build(BuildContext context) {    
    return Container(width: double.infinity, height: double.infinity, color: Color(GoEngColors.violet));
  }
}