Provider with watch can not run listen's lambda when app is in background.

[xiaochacha]

Describe the bug I have a stateProvider. And I have a Provider that watches stateProvider. When app is foreground, provider and stateProvider can listen and run successfully. But when I turn the app to background, only stateProvider can run listen's lambda, Provider can't run listen's lambda.

To Reproduce

import 'dart:async';

import 'package:flutter/material.dart';
import 'package:flutter_riverpod/flutter_riverpod.dart';

void main() => runApp(const ProviderScope(
      child: RiverpodProviderApp(),
    ));

class RiverpodProviderApp extends ConsumerStatefulWidget {
  const RiverpodProviderApp({Key? key}) : super(key: key);

  @override
  ConsumerState createState() => _RiverpodProviderAppState();
}

final stateProvider = StateProvider<int>((ref) => 0);
final provider = Provider<int>((ref) => ref.watch(stateProvider));

class _RiverpodProviderAppState extends ConsumerState<RiverpodProviderApp> {
  @override
  void initState() {
    super.initState();
    Timer.periodic(const Duration(seconds: 2), (timer) {
      final stateNotifier = ref.read(stateProvider.notifier);
      final value = stateNotifier.state;
      stateNotifier.state = value + 1;
    });
  }

  @override
  Widget build(BuildContext context) {
    ref.listen(provider, (previous, next) {
      print('provider previous:$previous, next:$next');
    });
    ref.listen(stateProvider, (previous, next) {
      print('stateProvider previous:$previous, next:$next');
    });
    return Container();
  }
}

Expected behavior When the exmple app run in foreground, both listen successfully.

I/flutter (12055): stateProvider previous:62, next:63
I/flutter (12055): provider previous:62, next:63
I/flutter (12055): stateProvider previous:63, next:64
I/flutter (12055): provider previous:63, next:64
I/flutter (12055): stateProvider previous:64, next:65
I/flutter (12055): provider previous:64, next:65

But when the exmple app run in background, only stateProvider listen successfully.

I/flutter (12055): stateProvider previous:305, next:306
I/flutter (12055): stateProvider previous:306, next:307
I/flutter (12055): stateProvider previous:307, next:308
I/flutter (12055): stateProvider previous:308, next:309
I/flutter (12055): stateProvider previous:309, next:310
I/flutter (12055): stateProvider previous:310, next:311
I/flutter (12055): stateProvider previous:311, next:312
I/flutter (12055): stateProvider previous:312, next:313

I guess the reason is that provider's update depend on drawFrame, but when app is in background, drawFrame not call. Can you give some suggestion or solution?

[xiaochacha]

@rrousselGit Can give some suggestion or solution?

[rrousselGit]

Providers are in sync with the app. If the app is paused, providers are paused too.

You'd have to manually read the provider. Then it would forcibly be updated

[xiaochacha]

@rrousselGit I want to handle server push when app is in background. I will update the stateProvider, but Provider who watch it can't listen the changes. What is the best way to solve it?

[rrousselGit]

As I said, reading the provider will cause it to rebuild. You could do that when your app is in background

[rrousselGit]

It's not really a bug. So I'll close it.

But if desired, we could have a flag for disabling this behavior. Feel free to open a new issue if you want it. I don't plan on working on it though