Belongs to medium article

main_screen.dart

class MainScreen extends StatefulWidget {
  State createState() => MainScreenState();
}

class MainScreenState extends State<MainScreen> {
  var _androidAppRetain = MethodChannel("android_app_retain");

  @override
  void initState() {
    super.initState();

    if (Platform.isAndroid) {
      _androidAppRetain.invokeMethod("wasActivityKilled").then((result){
        if (result){
          showDialog(
              context: context,
              builder: (context) {
                return ActivityGotKilledDialog();
              });
        }
      });
    }
  }

  Widget build(BuildContext context) {
    return WillPopScope(
      onWillPop: () {
        if (Platform.isAndroid) {
          if (Navigator.of(context).canPop()) {
            return Future.value(true);
          } else {
            _androidAppRetain.invokeMethod("sendToBackground");
            return Future.value(false);
          }
        } else {
          return Future.value(true);
        }
      },
      child: Scaffold(
        drawer: MainDrawer(),
        body: Stack(
          children: <Widget>[
            GoogleMap(),
          ],
        ),
      ),
    );
  }
}