void main() async {
     await Firebase.initializeApp();
     runApp(FlutterAnalyticsApp());
     }

    FirebaseAnalytics analytics = FirebaseAnalytics();
    FirebaseAnalyticsObserver observer = FirebaseAnalyticsObserver(analytics: analytics);

   MaterialApp(
   -------------
     navigatorObservers: <NavigatorObserver>[observer],
     -------------
   );

     await analytics.logEvent(
     name: 'item',
         parameters: <String, dynamic>{
           'price': price,
           'itemName': itemName,
           'quantity': quantity,
           'bool': addedToCart,
         },
     );

    As Events in Google/Firebase analytics takes around 24 hrs to reflect, so in order to test while developing make sure that you 
    run a debug build. Below is the link how you can do so.