How do I keep background tasks running when the app goes to the background on Flutter Android?

Question

I have an application for a (specific) company that has some tasks for the purpose of counting time, marking macros and generating notifications (electronic point type).

When the app gets too long in the background, sometimes android freezes the tasks and the app can’t generate the notifications at the time it should occur. When the app comes back to the foreground, td fixes itself and notifications are shown retroactively.

How to get around this situation?

---

I found a viable solution!

Analyzing the site https://dontkillmyapp.com/ I noticed that many also go through this same problem, besides seeing some solutions ideas. After comparing the solutions to the different manufacturers, I saw that some apps that have this notification in the background already have this qnd configuration are installed.

Searching how to "force" this setting, I arrived at the following solution:

pubspec.yaml

  android_power_manager: ^0.1.6
  permission_handler: ^5.0.1+1

Function:

void init() async {
    var status = await Permission.ignoreBatteryOptimizations.status;
    print("status: $status");
    if (status.isGranted) {
      print(
          "isIgnoring: ${(await AndroidPowerManager.isIgnoringBatteryOptimizations)}");
      if (!(await AndroidPowerManager.isIgnoringBatteryOptimizations)) {
        AndroidPowerManager.requestIgnoreBatteryOptimizations();
      }
    } else {
      Map<Permission, PermissionStatus> statuses = await [
        Permission.ignoreBatteryOptimizations,
      ].request();
      print(
          "permission value: ${statuses[Permission.ignoreBatteryOptimizations]}");
      if (statuses[Permission.ignoreBatteryOptimizations].isGranted) {
        AndroidPowerManager.requestIgnoreBatteryOptimizations();
      } else {
        exit(0);
      }
    }
  }

Appwidget.Dart (main)

  @override
  Widget build(BuildContext context) {
    init();

    SystemChrome.setPreferredOrientations([
      DeviceOrientation.portraitUp,
      DeviceOrientation.portraitDown,
    ]);
    DataTransferService().initTimerTask();
    return MaterialApp(
      navigatorKey: Modular.navigatorKey,
      title: APP_NAME,
      theme: ThemeData(
        primarySwatch: Colors.green,
      ),
      initialRoute: '/',
      routes: {
        '/': (context) => LoginPage(),
        '/home': (context) => HomePage(),
        '/notification': (context) => NotificationPage(),
        '/alerts': (context) => AlertsPage(),
      },
      onGenerateRoute: Modular.generateRoute,
    );
  }

With this, it asks for permission (if necessary) and, if you have permission, already generates the popup for the user to allow the app to be exception in battery optimization.

Now the notifications are coming straight! =]