Concurrents Jobs

[netofontess]

Example BackgroundFetch

• Plugin version: 0.5.4
• Platform: Android
• OS version: 9
• Device manufacturer / model: Android Emulator
• Flutter info (flutter info, flutter doctor): ✓] Flutter (Channel stable, v1.12.13+hotfix.8, on Mac OS X 10.15.3 19D76, locale pt-BR)

[✓] Android toolchain - develop for Android devices (Android SDK version 29.0.2) [✓] Xcode - develop for iOS and macOS (Xcode 11.3.1) [✓] Android Studio (version 3.5) [✓] VS Code (version 1.42.1) [✓] Connected device (1 available)

• No issues found!

• Plugin config

import 'dart:async';
import 'dart:convert';
import 'package:flutter/material.dart';
import 'package:flutter/services.dart';

import 'package:shared_preferences/shared_preferences.dart';
import 'package:background_fetch/background_fetch.dart';

const EVENTS_KEY = "fetch_events";

/// This "Headless Task" is run when app is terminated.
void backgroundFetchHeadlessTask() async {
  print('[BackgroundFetch] Headless event received.');

  SharedPreferences prefs = await SharedPreferences.getInstance();

  var count = 1;
  while (1 == 1) {
    await new Future.delayed(const Duration(seconds: 2), () => "1");
    print(count);
    count++;
  }

  BackgroundFetch.finish();
}

void main() {
  // Enable integration testing with the Flutter Driver extension.
  // See https://flutter.io/testing/ for more info.
  runApp(new MyApp());

  // Register to receive BackgroundFetch events after app is terminated.
  // Requires {stopOnTerminate: false, enableHeadless: true}
  BackgroundFetch.registerHeadlessTask(backgroundFetchHeadlessTask);
}

class MyApp extends StatefulWidget {
  @override
  _MyAppState createState() => new _MyAppState();
}

class _MyAppState extends State<MyApp> {
  bool _enabled = true;
  int _status = 0;
  List<String> _events = [];

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

  // Platform messages are asynchronous, so we initialize in an async method.
  Future<void> initPlatformState() async {
    // Load persisted fetch events from SharedPreferences
    SharedPreferences prefs = await SharedPreferences.getInstance();
    String json = prefs.getString(EVENTS_KEY);
    if (json != null) {
      setState(() {
        _events = jsonDecode(json).cast<String>();
      });
    }

    // Configure BackgroundFetch.
    BackgroundFetch.configure(
            BackgroundFetchConfig(
                minimumFetchInterval: 15,
                stopOnTerminate: false,
                startOnBoot: true,
                enableHeadless: true,
                requiresBatteryNotLow: false,
                requiresCharging: false,
                requiresStorageNotLow: false,
                requiresDeviceIdle: false,
                requiredNetworkType: BackgroundFetchConfig.NETWORK_TYPE_NONE),
            _onBackgroundFetch)
        .then((int status) {
      print('[BackgroundFetch] configure success: $status');
      setState(() {
        _status = status;
      });
    }).catchError((e) {
      print('[BackgroundFetch] configure ERROR: $e');
      setState(() {
        _status = e;
      });
    });

    // Optionally query the current BackgroundFetch status.
    int status = await BackgroundFetch.status;
    setState(() {
      _status = status;
    });

    // If the widget was removed from the tree while the asynchronous platform
    // message was in flight, we want to discard the reply rather than calling
    // setState to update our non-existent appearance.
    if (!mounted) return;
  }

  void _onBackgroundFetch() async {
    SharedPreferences prefs = await SharedPreferences.getInstance();

    // This is the fetch-event callback.
    print('[BackgroundFetch] Event received');

    var count = 1;
    while (1 == 1) {
      await new Future.delayed(const Duration(seconds: 2), () => "1");
      print(count);
      count++;
    }

    // IMPORTANT:  You must signal completion of your fetch task or the OS can punish your app
    // for taking too long in the background.
    BackgroundFetch.finish();
  }

  void _onClickEnable(enabled) {
    setState(() {
      _enabled = enabled;
    });
    if (enabled) {
      BackgroundFetch.start().then((int status) {
        print('[BackgroundFetch] start success: $status');
      }).catchError((e) {
        print('[BackgroundFetch] start FAILURE: $e');
      });
    } else {
      BackgroundFetch.stop().then((int status) {
        print('[BackgroundFetch] stop success: $status');
      });
    }
  }

  void _onClickStatus() async {
    int status = await BackgroundFetch.status;
    print('[BackgroundFetch] status: $status');
    setState(() {
      _status = status;
    });
  }

  void _onClickClear() async {
    SharedPreferences prefs = await SharedPreferences.getInstance();
    prefs.remove(EVENTS_KEY);
    setState(() {
      _events = [];
    });
  }

  @override
  Widget build(BuildContext context) {
    const EMPTY_TEXT = Center(
        child: Text(
            'Waiting for fetch events.  Simulate one.\n [Android] \$ ./scripts/simulate-fetch\n [iOS] XCode->Debug->Simulate Background Fetch'));

    return new MaterialApp(
      home: new Scaffold(
        appBar: new AppBar(
            title: const Text('BackgroundFetch Example',
                style: TextStyle(color: Colors.black)),
            backgroundColor: Colors.amberAccent,
            brightness: Brightness.light,
            actions: <Widget>[
              Switch(value: _enabled, onChanged: _onClickEnable),
            ]),
        body: (_events.isEmpty)
            ? EMPTY_TEXT
            : Container(
                child: new ListView.builder(
                    itemCount: _events.length,
                    itemBuilder: (BuildContext context, int index) {
                      String timestamp = _events[index];
                      return InputDecorator(
                          decoration: InputDecoration(
                              contentPadding: EdgeInsets.only(
                                  left: 5.0, top: 5.0, bottom: 5.0),
                              labelStyle:
                                  TextStyle(color: Colors.blue, fontSize: 20.0),
                              labelText: "[background fetch event]"),
                          child: new Text(timestamp,
                              style: TextStyle(
                                  color: Colors.black, fontSize: 16.0)));
                    }),
              ),
        bottomNavigationBar: BottomAppBar(
            child: Container(
                padding: EdgeInsets.only(left: 5.0, right: 5.0),
                child: Row(
                    mainAxisAlignment: MainAxisAlignment.spaceBetween,
                    children: <Widget>[
                      RaisedButton(
                          onPressed: _onClickStatus,
                          child: Text('Status: $_status')),
                      RaisedButton(
                          onPressed: _onClickClear, child: Text('Clear'))
                    ]))),
      ),
    );
  }
}

To Reproduce Steps to reproduce the behavior:

1. I just force the background to start

Hi! Tk's for this plugin.

I have a problem with competing tasks, mainly at Headless. When I start BackgroundFetch Headless and open the application and force BackgroundFetch again it does not recognize that there is a task running and starts another one. Was he supposed to identify that? If I force a HeadLess and while running force another, it will also start another one without stopping the previous one.

Obs: I used the example in the repository to simulate this action.

[christocracy]

I don't know if there's anything that can be done about that rare edge-case.

[netofontess]

I don't know if there's anything that can be done about that rare edge-case.

Should he understand that there is another job running? I simple copied your example and add in the while loop...

[christocracy]

After some research, I should be able to detect whether Android has an existing task scheduled.

[github-actions[bot]]

This issue is stale because it has been open for 30 days with no activity.

[github-actions[bot]]

This issue was closed because it has been inactive for 14 days since being marked as stale.