I have an asynchronous function for checking internet access which is in another file. Here is its code:

//Check User Connection
class CheckUserConnection {

  Future checkInternetAvailability() async {
    try {
      final result = await InternetAddress.lookup('example.com');
      if (result.isNotEmpty && result[0].rawAddress.isNotEmpty) {
        return true;
      }
    } on SocketException catch (_) {
      return false;
    }
  }
}

I need it to be activated when a button is pressed in the main menu. Here is the code for this screen:

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

class MyApp extends StatelessWidget {
  const MyApp({Key? key}) : super(key: key);

  static const String _title = 'Example';

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: _title,
        home: Container(
            child: Scaffold(
        appBar: AppBar(title: const Text(_title)),
        // body: const MyStatelessWidget(),
              body: const MainWidget(),
      ),
    )
    );
  }
}

// class MyStatelessWidget extends StatelessWidget {
//   const MyStatelessWidget({Key? key}) : super(key: key);
class MainWidget extends StatefulWidget {
  const MainWidget({Key? key}) : super(key: key);

  @override
  State<MainWidget> createState() => _MainWidgetState();
}

class _MainWidgetState extends State<MainWidget> {

  @override
  Widget build(BuildContext context) {
    InternetDialogHandler _internetDialogHandler = InternetDialogHandler();
    CheckUserConnection _checkUserConnection = CheckUserConnection();
    bool _internetAvailable = await _checkUserConnection.checkInternetAvailability();
    // bool _internetAvailable = false;
    return Center(
      child: Column(
        mainAxisSize: MainAxisSize.max,
        mainAxisAlignment: MainAxisAlignment.spaceBetween,
        children: <Widget>[
          Column(
            children: [
              GradientButton(label: 'New Game', onTap: () {
                Navigator.push(
                  context,
                  MaterialPageRoute(builder: (context) => const NewGameRoute()),
                );
              }),
              GradientButton(label: 'Continue Game', onTap: () {
                if(_internetAvailable)
                {
                  //do something here;
                  Navigator.push(
                    context,
                    MaterialPageRoute(builder: (context) => const NewGameRoute()),
                  );
                } else{
                  //handle no internet here
                  _internetDialogHandler.showInternetDialog(context);
                }



              }),
            ],
          ),
          Column(
            children: [
              GradientButton(label: 'Back Button', onTap: () {
                Navigator.push(
                  context,
                  MaterialPageRoute(builder: (context) => const BackRoute()),
                );



                // print('Button 1');



              }),
              GradientButton(label: 'Button 2', onTap: () {print('Button 2');}),
              GradientButton(label: 'Internet', onTap: () {
                Navigator.push(
                  context,
                  MaterialPageRoute(builder: (context) => const InternetRoute()),
                );
              }),
            ],
          )
        ],
      ),
    );
  }
}

But the problem is that when I paste:

bool _internetAvailable = await _checkUserConnection.checkInternetAvailability();

I get an error:

The await expression can only be used in an async function.

Why? Async is already in that function, which is in another file. Where else do I need to add async in my main page code?

I've been given advice:

In initstate just call a method. And in that method add async and check internrt and set state based on internet availability 

But since I'm a beginner, I don't understand what exactly I should do.

CodePudding user response：

Add an initstate to the stateful widget. Inside the initstate add this code

checkInternet();

Then define a function

checkInternet() async{
bool internetAvaibale = await _checkInternetConnection.checkInternetAvailability();
if(internetAvailable)//do something here and setstate
else // show no internet screen and setstate
}

CodePudding user response：

you called bool _internetAvailable = await _checkUserConnection.checkInternetAvailability(); in build method, In the event that build method can't async.

you must be do like below code:

class _MainWidgetState extends State<MainWidget> {
   bool? _internetAvailable;

   void checkNet() async{
   _internetAvailable = await 
   _checkUserConnection.checkInternetAvailability();
  
   // can you do any async operation into this method, Just be careful to check it
   }

  @overrider
  void initState(){
   super.initState();
   checkNet();
  }

  @override
  Widget build(BuildContext context) {
    ....
    return _internetAvailable == null?
    CupertinoActivityIndicator()//loading
    :Center(
      child: Column(
    ....