background_fetch 0.3.0

Periodic callbacks in the background for both iOS and Android. Includes Android Headless implementation.

example/lib/main.dart

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();

  // Read fetch_events from SharedPreferences
  List<String> events = [];
  String json = prefs.getString(EVENTS_KEY);
  if (json != null) {
    events = jsonDecode(json).cast<String>();
  }
  // Add new event.
  events.insert(0, new DateTime.now().toString() + ' [Headless]');
  // Persist fetch events in SharedPreferences
  prefs.setString(EVENTS_KEY, jsonEncode(events));

  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');
    setState(() {
      _events.insert(0, new DateTime.now().toString());
    });
    // Persist fetch events in SharedPreferences
    prefs.setString(EVENTS_KEY, jsonEncode(_events));

    // 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'))
                ]
            )
          )
        ),
      ),
    );
  }
}