android - How to make Flutter Workmanager plugin and Location plugin work together

Question

1. Problem description

My goal is to build a Flutter app that gets periodic location updates using this workmanager plugin and using this location plugin. But I can't get the Location plugin to be loaded properly when my Workmanager callback fires. I get this error:

MissingPluginException(No implementation found for method getLocation on channel lyokone/location)

So basically, the problem is that when the Workmanager plugin tries to run dart code, it doesn't load up the Location plugin.

2. Other resources I have researched

I found others facing the same issue, here, here, and here.

As far as I understand, the solution provided to these questions boils down to: create a file named CustomApplication.java, which extends FlutterApplication, and which registers your plugin(s). And then register the CustomApplication.java file inside you AndoidManifest.xml file.

3. My code thus far

I have tried to make a bare-minimum app that implements the features I require:

1. I implemented Workmanager plugin (works fine)
2. I implemented Location plugin (works fine)
3. I attempted to combine these features (does not work)

To see exactly what I have done at each step, please look here: https://gitlab.com/tomoerlemans/workmanager_with_location/-/commits/master. (This repository can also be used to quickly replicate the issue).

The relevant code files are as follows:

main.dart

import 'package:flutter/material.dart';
import 'package:workmanager/workmanager.dart';
import 'package:location/location.dart';

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: MyHomePage(),
    );
  }
}

class MyHomePage extends StatefulWidget {
  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            RaisedButton(
              onPressed: () {
                Workmanager.registerPeriodicTask(
                    "1", "simpleTask");
              },
              child: Text("Start workmanager"),
            ),
            RaisedButton(
              onPressed: () {
                getLocation();
              },
              child: Text("Get current location"),
            ),
          ],
        ),
      ),
    );
  }
}

void callbackDispatcher() {
  Workmanager.executeTask((task, inputData) {
    print("Native called background task at ${DateTime.now().toString()}");
    getLocation();
    return Future.value(true);
  });
}

void getLocation() async {
  LocationData currentLocation;
  var location = new Location();
  try {
    currentLocation = await location.getLocation();
  } on Exception catch (e) {
    print("Error obtaining location: $e");
    currentLocation = null;
  }
  print("Location altitude: ${currentLocation.altitude}");
  print("Location longitude: ${currentLocation.longitude}");
}

pubspec.yaml

name: background_location
description: A new Flutter project.

version: 1.0.0+1

environment:
  sdk: ">=2.1.0 <3.0.0"

dependencies:
  flutter:
    sdk: flutter

  cupertino_icons: ^0.1.2
  workmanager: ^0.2.0
  location: ^2.3.5


dev_dependencies:
  flutter_test:
    sdk: flutter

flutter:
  uses-material-design: true

CustomApplication.java

package io.flutter.plugins;

import io.flutter.app.FlutterApplication;
import io.flutter.plugin.common.PluginRegistry;
import io.flutter.plugin.common.PluginRegistry.PluginRegistrantCallback;
import io.flutter.plugins.GeneratedPluginRegistrant;
import be.tramckrijte.workmanager.WorkmanagerPlugin;
import com.lyokone.location.LocationPlugin;

public class CustomApplication extends FlutterApplication implements PluginRegistry.PluginRegistrantCallback {
    @Override
    public void onCreate() {
        super.onCreate();
        WorkmanagerPlugin.setPluginRegistrantCallback(this);

    }
    @Override
    public void registerWith(PluginRegistry registry) {
        WorkmanagerPlugin.registerWith(registry.registrarFor("be.tramckrijte.workmanager.WorkmanagerPlugin"));
        LocationPlugin.registerWith(registry.registrarFor("com.lyokone.location.LocationPlugin"));
    }
}

AndroidManifest.xml

<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.background_location">        
    <uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" />

    <application
        android:name="io.flutter.plugins.CustomApplication"
        android:label="background_location"
        android:icon="@mipmap/ic_launcher">
        <activity
            android:name=".MainActivity"
            android:launchMode="singleTop"
            android:theme="@style/LaunchTheme"
            android:configChanges="orientation|keyboardHidden|keyboard|screenSize|smallestScreenSize|locale|layoutDirection|fontScale|screenLayout|density|uiMode"
            android:hardwareAccelerated="true"
            android:windowSoftInputMode="adjustResize">
            <intent-filter>
                <action android:name="android.intent.action.MAIN"/>
                <category android:name="android.intent.category.LAUNCHER"/>
            </intent-filter>
        </activity>
        <meta-data
            android:name="flutterEmbedding"
            android:value="2" />
    </application>
</manifest>

Finally, I am running the following versions of Dart/Flutter/etc:

Flutter 1.12.13+hotfix.5 ? channel stable ? https://github.com/flutter/flutter.git
Framework ? revision 27321ebbad (10 weeks ago) ? 2019-12-10 18:15:01 -0800
Engine ? revision 2994f7e1e6
Tools ? Dart 2.7.0

Answer 1

I haven't tried what background location tracking but considering you only want location tracking from background then I think workmanager + geolocater would work. You should see this project ha_client it's using workmanager and geolocater together to get the coords

Also the location package you're using has it's own background location tracking which is in experimental Background Location Updates.