MissingPluginException "No implementation found for method" in path_provider when called from isolate

E/flutter ( 9978): [ERROR:flutter/lib/ui/ui_dart_state.cc(198)] Unhandled Exception: MissingPluginException(No implementation found for method getApplicationDocumentsDirectory on channel plugins.flutter.io/path_provider)
E/flutter ( 9978): #0 MethodChannel._invokeMethod (package:flutter/src/services/platform_channel.dart:165:7)
E/flutter ( 9978):
E/flutter ( 9978): #1 getApplicationDocumentsDirectory (package:path_provider/path_provider.dart:115:24)
E/flutter ( 9978):
E/flutter ( 9978): #2 onBackgroundStart (package:szwmobiletracker/main.dart:135:19)
E/flutter ( 9978):
E/flutter ( 9978):

Just updated to path_provider version 2.0.9

Please use the issue template when filing issues; your report is missing a lot of information that is requested in the template.

What version of Flutter are you using? What platform is this on? What is the complete reproducible test case?

And it worked before............

We still need a reproducible case.

And it worked before............

There was a recent change to path_provider_android, but to understand what the issue with that change is we need a reproducible test case.

But I'm not willing to share my complete program publicly. And I have no time to produce a dummy with the same issue.
I just did a full flutter pub upgrade. These are the packages I use:

import 'dart:async';
import 'dart:io';
import 'dart:convert';
import 'package:intl/intl.dart';
import 'package:geolocator/geolocator.dart';
import 'package:flutter/material.dart';
import 'package:qr_code_scanner/qr_code_scanner.dart';
import 'package:http/http.dart' as http;
import 'package:uuid/uuid.dart';
import 'package:flutter_background_service/flutter_background_service.dart';
import 'package:path_provider/path_provider.dart';
import 'package:path/path.dart' as p;

The stack trace with filenames and line numbers should provide enough insight for the experts to find where the issue is:

E/flutter ( 9978): [ERROR:flutter/lib/ui/ui_dart_state.cc(198)] Unhandled Exception: MissingPluginException(No implementation found for method getApplicationDocumentsDirectory on channel plugins.flutter.io/path_provider)
E/flutter ( 9978): #0 MethodChannel._invokeMethod (package:flutter/src/services/platform_channel.dart:165:7)
E/flutter ( 9978):
E/flutter ( 9978): https://github.com/flutter/flutter/pull/1 getApplicationDocumentsDirectory (package:path_provider/path_provider.dart:115:24)
E/flutter ( 9978):
E/flutter ( 9978): https://github.com/flutter/flutter/pull/2 onBackgroundStart (package:szwmobiletracker/main.dart:135:19)
E/flutter ( 9978):
E/flutter ( 9978):

And I have no time to produce a dummy with the same issue.

We need reproducible test cases to investigate issues. See https://github.com/flutter/flutter/wiki/Issue-hygiene#issues-should-have-clear-steps-to-reproduce and https://github.com/flutter/flutter/wiki/Issue-hygiene#issues-should-have-clear-steps-to-reproduce

We have automated tests that use path_provider, and they pass. Your use case is clearly different in some way; without knowing how, we can't investigate.

The stack trace with filenames and line numbers should provide enough insight for the experts to find where the issue is

It isn't, because we don't know anything about what szwmobiletracker/main.dart:135 is doing. For instance, whether or not it is running in an isolate is likely important here, and we have absolutely no way to determine that from the information you have provided.

The call to path_provider ( Directory dir = await getApplicationDocumentsDirectory(); ) is indeed done from a background process, started using the flutter_background_service package.

Here is the code of an app giving exactly the same result when calling the path_provider from the background process.

Details

import 'dart:async';
import 'dart:io';
import 'package:flutter/material.dart';
import 'package:flutter_background_service/flutter_background_service.dart';
import 'package:path_provider/path_provider.dart';
import 'package:path/path.dart' as p;

late File dataFile;
Timer bgEventTimer = Timer.periodic(const Duration(seconds: 15), (timer) {  }); // without a function, so it is actually cancelled

Future main() async {
  WidgetsFlutterBinding.ensureInitialized();
  //
  // get the file path
  Directory dir = await getApplicationDocumentsDirectory();
  dataFile = File(p.join(dir.path, 'bgData.txt'));
  //
  await initializeBackgroundService();
  //
  runApp(const MyApp());
}

Future<void> initializeBackgroundService() async {
  final backgroundService = FlutterBackgroundService();
  await backgroundService.configure(
    androidConfiguration: AndroidConfiguration(
      // auto start service
      autoStart: true,
      // this will executed when app is in foreground or background in separated isolate
      onStart: onBackgroundStart,
      // true means that notification arte visible
      isForegroundMode: true,
    ),
    iosConfiguration: IosConfiguration(
      // auto start service
      autoStart: true,
      // this will executed when app is in foreground in separated isolate
      onForeground: onBackgroundStart,
      // you have to enable background fetch capability on xcode project
      onBackground: onBackgroundStart,
    ),
  );
}

void onBackgroundStart() async {
  WidgetsFlutterBinding.ensureInitialized();
  bgEventTimer.cancel(); // just in case we were still running
  final backgroundService = FlutterBackgroundService();
  Directory dir = await getApplicationDocumentsDirectory();
  File bgDataFile = File(p.join(dir.path, 'bgData.txt'));
  // just in case we started without a bgData file....
  if (bgDataFile.existsSync() == false) {
    backgroundService.stopBackgroundService(); // just exit the background service
    return;
  }
  //
  // start our timer job (after we defined it)
  //
  void bgTimerJob () async {
  }
  //
  bgEventTimer = Timer.periodic(const Duration(seconds: 1), (timer) { bgTimerJob(); });
}

class MyApp extends StatelessWidget {
  const MyApp({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Path Provider test',
      theme: ThemeData(
        primarySwatch: Colors.green,
      ),
      home: const MyHomePage(title: 'Path Provider test'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  const MyHomePage({Key? key, required this.title}) : super(key: key);
  final String title;
  @override
  State<MyHomePage> createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> with WidgetsBindingObserver {

  @override
  void initState() {
    super.initState();
  }

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

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
          title: Text(widget.title),
      ),
      body: Center(
        child: Stack(
        ),
      ), // This trailing comma makes auto-formatting nicer for build methods.
    );
  }


}

By the way, I used shared_preferences before, but that gave the same problems in combination with the background service. I really do need to store info in a file in the background, also when the foreground is not running (could use the background sendData method, but where does that go when the foreground is not active?)

This is due to #98591 then, and is the path_provider version of #98473.

The workaround described there will work for path_provider as well:

Add dependencies on path_provider_android and path_provider_ios.

At the beginning of your background isolate entry point, add something like:

if (Platform.isAndroid) PathProviderAndroid.registerWith();
if (Platform.isIOS) PathProviderIOS.registerWith();

Ok, that works! Thanks!!

The longer-term solution is that anything setting up an isolate where plugins are expected to work should call DartPluginRegistrant.ensureInitialized(), which will run all Dart plugin registration (similar to how they already need to call WidgetsFlutterBinding.ensureInitialized() to make platform message work in the first place). That's not currently on stable yet though, as it only just landed on master.

To summarize the solution: at the start of the entry point for any isolate that needs to use plugins (where you are presumably already calling WidgetsFlutterBinding.ensureInitialized()):

For Flutter 2.11+ (currently master), call DartPluginRegistrant.ensureInitialized(), which will run the Dart plugin registration for all plugins that need it.
For older versions of Flutter, manually call the registerWith of any plugin implementations you use that have Dart registration. For path_provider, see above for details.

Since the plan going forward is to require DartPluginRegistrant.ensureInitialized() in isolates, closing as fixed.

This thread has been automatically locked since there has not been any recent activity after it was closed. If you are still experiencing a similar issue, please open a new bug, including the output of flutter doctor -v and a minimal reproduction of the issue.

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MissingPluginException "No implementation found for method" in path_provider when called from isolate #99155

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MissingPluginException "No implementation found for method" in path_provider when called from isolate #99155

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stuartmorgan-g commented on Feb 25, 2022

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