Observing Flutter application lifecycle changes

The application lifecycle describes the host application’s relationship to its platform and views. It is separate from whether one route is covered by another.

The original observer was:

import 'package:flutter/material.dart';
import 'package:nft/utils/app_log.dart';

class HomePage extends StatefulWidget {
  const HomePage({Key key}) : super(key: key);

  @override
  _HomePageState createState() => _HomePageState();
}

class _HomePageState extends State<HomePage>
    with WidgetsBindingObserver {
  @override
  void initState() {
    super.initState();
    WidgetsBinding.instance.addObserver(this);
  }

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

  @override
  void didChangeAppLifecycleState(AppLifecycleState state) {
    /// Log app life cycle state
    logger.d(state);
  }

  @override
  Widget build(BuildContext context) {
    return Container();
  }
}

Its earlier interaction trace was:

- App is opening
- Press home
flutter: [D]  AppLifecycleState.inactive
flutter: [D]  AppLifecycleState.paused

- Open app by tap on app icon
flutter: [D]  AppLifecycleState.inactive
flutter: [D]  AppLifecycleState.resumed

- In recent application (double home tap on iPhone)
flutter: [D]  AppLifecycleState.inactive

- Kill app from recent application
flutter: [D]  AppLifecycleState.paused

The note also recorded this explanation of detached:

When the application is in this state, the engine is running without a view. It can either be in the progress of attaching a view when engine was first initializes, or after the view being destroyed due to a Navigator pop. -Flutter-

An engine without an attached view is not the same thing as an ordinary screen losing route focus. Platform behavior and available lifecycle states vary by framework generation. Registration, removal, and the owning state’s lifetime should be reviewed together. No foreground/background transitions were generated for this revision.

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