How to execute code before app exit flutter

You can not do exactly what you want to do right now, anyway, the best approach right now is to check when the application it’s running in background/inactive using the AppLifecycleState from the SDK (basically does what your library is trying to do)

The library that you are using it’s outdated, since a pull request from November 2019 the AppLifecycleState.suspending it’s called AppLifecycleState.detached.

You can take a look at the AppLifecycleState enum in the api.flutter.dev website

Here’s an example of how to observe the lifecycle status of the containing activity:

import 'package:flutter/widgets.dart';

class LifecycleWatcher extends StatefulWidget {
  @override
  _LifecycleWatcherState createState() => _LifecycleWatcherState();
}

class _LifecycleWatcherState extends State<LifecycleWatcher> with WidgetsBindingObserver {
  AppLifecycleState _lastLifecycleState;

  @override
  void initState() {
    super.initState();
    WidgetsBinding.instance.addObserver(this);
  }

  @override
  void dispose() {
    WidgetsBinding.instance.removeObserver(this);
    super.dispose();
  }

  @override
  void didChangeAppLifecycleState(AppLifecycleState state) {
    setState(() {
      _lastLifecycleState = state;
    });
  }

  @override
  Widget build(BuildContext context) {
    if (_lastLifecycleState == null)
      return Text('This widget has not observed any lifecycle changes.', textDirection: TextDirection.ltr);

    return Text('The most recent lifecycle state this widget observed was: $_lastLifecycleState.',
        textDirection: TextDirection.ltr);
  }
}

void main() {
  runApp(Center(child: LifecycleWatcher()));
}

I think that deleting your data on the inactive cycle and then creating it again in the resumed one can work for you.