Downloads sometimes fail with error message: `flutter: not found task corresponding to given task id`

On both Android and iOS, downloads sometimes fail with this error message: flutter: not found task corresponding to given task id

I found that running flutter clean and rebuilding the app seems to make this disappear for a bit (download successful and file can be opened in relevant applications), but when I build the app again after changing something, the error returns. I’ve enabled Android cleartext traffic, to no avail.

Here’s a minimal reproduction of my code:

import 'dart:isolate';
import 'dart:ui';

import 'package:flutter/material.dart';
import 'package:flutter_downloader/flutter_downloader.dart';
import 'package:path_provider/path_provider.dart';

void main(){
  _initializeFlutterDownloader();
  runApp(MyApp());
}

_initializeFlutterDownloader()async{
    WidgetsFlutterBinding.ensureInitialized();
await FlutterDownloader.initialize();
}

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Downloader Example',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(title: 'Flutter Downloader Example'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);
  final String title;

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

class _MyHomePageState extends State<MyHomePage> {
  ReceivePort _port = ReceivePort();
  
  @override
  void initState() {
    super.initState();
    _downloadListener();
  }

  static void downloadCallback(
      String id, DownloadTaskStatus status, int progress) {
    final SendPort send =
        IsolateNameServer.lookupPortByName('downloader_send_port');
    send.send([id, status, progress]);
  }

  _downloadListener() {
    IsolateNameServer.registerPortWithName(
        _port.sendPort, 'downloader_send_port');
    _port.listen((dynamic data) {
      String id = data[0];
      DownloadTaskStatus status = data[1];
      if (status.toString() == "DownloadTaskStatus(3)") {
        FlutterDownloader.open(taskId: id);
      }
    });
    FlutterDownloader.registerCallback(downloadCallback);
  }

  void _download() async {
    String _localPath =
        (await findLocalPath()) + Platform.pathSeparator + 'Example_Downloads';

    final savedDir = Directory(_localPath);
    bool hasExisted = await savedDir.exists();
    if (!hasExisted) {
      savedDir.create();
    }
    String _url =
        "https://www.colonialkc.org/wp-content/uploads/2015/07/Placeholder.png";
    final download = await FlutterDownloader.enqueue(
      url: _url,
      savedDir: _localPath,
      showNotification: true,
      openFileFromNotification: true,
    );
  }

  Future<String> findLocalPath() async {
    final directory =
        // (MyGlobals.platform == "android")
        // ?
        await getExternalStorageDirectory();
    // : await getApplicationDocumentsDirectory();
    return directory.path;
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
          ],
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: _download,
        child: Icon(Icons.file_download),
      ), // This trailing comma makes auto-formatting nicer for build methods.
    );
  }
}

[BethshanDeveloper]

I have this same problem on iOS simulator. Thank you LaxmikanthMadhyastha for the Future.delayed fix - this seems to solve the problem for me. However, it’s a bit of a hack, and it would be nice if this could be solved in the package 😃

[rivetingpeppermint]

It appears that the tasks won’t run after I performed hot restart. After each build, everything works fine, but once I hot restart, none of the tasks would run.