🐞Calling callbackDispatcher freeze app UI

[Natzely]

Technology	Version
Workmanager version	0.8.0

Describe the error
When the workmanager calls the callbackDispatcher, the app UI freezes for a moment and any heavy work will continue to freeze it. It can be mitigated by using compute for the heavy computations, but the initial callbackDispatcher call will always freeze the UI. Seems like the initial call is still tied to the main isolate unlike the call with compute.

I've tried searching an answer to this everywhere but no luck. I've tested this in the example project by adding a CircularProgressIndicator() to the top of the of the column as well as created my own small one below. I believe this is leading to some weird interactions with the audio_session in my own app (though that's just speculation on my part).

I'm perfectly willing to accept I'm setting this all up wrong. If so, I'd love to what I'm doing wrong.

import 'dart:convert';

import 'package:flutter/material.dart';
import 'package:flutter/foundation.dart';
import 'package:xml/xml.dart';
import 'package:http/http.dart' as http;
import 'package:workmanager/workmanager.dart';

void main() {
  WidgetsFlutterBinding.ensureInitialized();
  Workmanager().initialize(
    callbackDispatcher,
    isInDebugMode: false,
  );
  runApp(const MyApp());
}

class MyApp extends StatelessWidget {
  const MyApp({super.key});

  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        colorScheme: ColorScheme.fromSeed(seedColor: Colors.deepPurple),
      ),
      home: const MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  const MyHomePage({super.key, required this.title});

  final String title;

  @override
  State<MyHomePage> createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {

  @override
  void initState() {
    // TODO: implement initState
    super.initState();
  }

  int _counter = 0;

  void registerTask(bool useCompute) {
    Workmanager().cancelAll();
    Workmanager().registerOneOffTask(
      'backgroundTask',
      'backgroundTask',
      initialDelay: const Duration(seconds: 2),
      existingWorkPolicy: ExistingWorkPolicy.replace,
      inputData: { 'useCompute': useCompute }
    );
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        backgroundColor: Theme.of(context).colorScheme.inversePrimary,
        title: Text(widget.title),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            ElevatedButton(
              onPressed: () => registerTask(false), 
              child: Text('Task without compute'),
            ),
            ElevatedButton(
              onPressed: () => registerTask(true), 
              child: Text('Task with compute'),
            ),
            CircularProgressIndicator(),
          ],
        ),
      ),
    );
  }
}

@pragma('vm:entry-point')
void callbackDispatcher() async {
  Workmanager().executeTask((task, inputData) async {
    final useCompute = inputData?['useCompute'] ?? false;
    if(useCompute) {
      compute<Map<String, dynamic>, void>(updateTask, inputData ?? {});
      return true;
    }
    else {
      await updateTask(inputData ?? {});
      return true;//Future.value(true);
    }
  });
}

updateTask(Map<String, dynamic> value) async {
  try{
  print('Start debug task');
  final url = r'https://feeds.libsyn.com/583795/rss?limit=10';
  final uri = Uri.parse(url);

  print('Create Response');
  final request = http.Request('GET', uri)..maxRedirects = 20;
  request.followRedirects = false;
  final response = await http.Client().send(request);
  final location = response.headers['location'];
  // snapShot = log('Check feed URL', stopwatch, snapShot);

  print('Http get');
  //final feedContent = await http.get(uri);
  final feedContent = await http.get(uri);
  // snapShot = log('Feed url get', stopwatch, snapShot);
  final decodedContent = Utf8Decoder().convert(feedContent.bodyBytes);
  //print('No XML');
  
  print('XML Parse');
  final feedDoc = XmlDocument.parse(decodedContent);
  // snapShot = log('Xml parse', stopwatch, snapShot);
  final parentNode = feedDoc.findElements('rss')
    .single.findElements('channel').single;

  print('Get title');
  final title = _getNodeValue(parentNode, 'title', 'Title Not Found');
  print(title);
  } catch (e) {
    print(e);
  }
  print('End debug task');  
}

String _getNodeValue(XmlElement parentNode, String nodeName, String backup) {
  try {
    var node = parentNode.findElements(nodeName);
    if (node.isNotEmpty) {
      var nodeText = node.first.innerText;
      return nodeText;
    } else
      return backup;
  } catch (_) {
    return backup;
  }
}

name: test_project
description: "A new Flutter project."
publish_to: 'none'
version: 1.0.0+1

environment:
  sdk: ^3.8.1

dependencies:
  flutter:
    sdk: flutter

  cupertino_icons: ^1.0.8
  xml: ^6.5.0
  http: ^1.4.0
  workmanager: ^0.8.0

dev_dependencies:
  flutter_test:
    sdk: flutter

  flutter_lints: ^5.0.0

flutter:
  uses-material-design: true

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