asyncFlutter.dart

//Put this code in the class which extens State class

static const platform = const MethodChannel('samples.flutter.dev/filesChannel'); //used to connect with Java/Kotlin
List<dynamic> fileNames = <dynamic>[];

Future<void> _invokeNativeFun(int flag) async {
    String s;
      try {
          if(flag == 0)
            fileNames = await platform.invokeMethod('getNames'); //getNames function called from Kotlin/Java
      } on PlatformException catch (e) {
          s = "Failed: '${e.message}'."; //you can print it
      }
}

@override
Widget build(BuildContext context) {
    return FutureBuilder(
      future: _invokeNativeFun(0),
      builder: (context, snapshot){
        if(snapshot.connectionState == ConnectionState.done){
          return ListView.builder(
            itemCount: fileNames.length,
            itemBuilder: (BuildContext context, int index) => buildBody(context, index),
          );
        } else {
          return Center(child: CircularProgressIndicator());
        }
      }
    );
  }
  
Widget buildBody(BuildContext context, int index){
      return Text(fileNames[index],style:TextStyle(fontSize:20.0));
}