cordova-plugin-background-fetch ·

By Transistor Software, creators of Cordova Background Geolocation

---

Background Fetch is a very simple plugin for iOS & Android which will awaken an app in the background about every 15 minutes, providing a short period of background running-time. This plugin will execute your provided callbackFn whenever a background-fetch event occurs.

There is no way to increase the rate which a fetch-event occurs and this plugin sets the rate to the most frequent possible — you will never receive an event faster than 15 minutes. The operating-system will automatically throttle the rate the background-fetch events occur based upon usage patterns. Eg: if user hasn't turned on their phone for a long period of time, fetch events will occur less frequently.

🆕 Background Fetch now provides a scheduleTask method for scheduling arbitrary "one-shot" or periodic tasks.

iOS

• There is no way to increase the rate which a fetch-event occurs and this plugin sets the rate to the most frequent possible — you will never receive an event faster than 15 minutes. The operating-system will automatically throttle the rate the background-fetch events occur based upon usage patterns. Eg: if user hasn't turned on their phone for a long period of time, fetch events will occur less frequently.
• scheduleTask seems only to fire when the device is plugged into power.

Android

• The Android plugin provides a Headless implementation allowing you to continue handling events even after app terminate.

Using the plugin

• Cordova / Ionic 1 The plugin creates the object window.BackgroundFetch.

• With Typescript (eg: Ionic 2+):

import BackgroundFetch from "cordova-plugin-background-fetch";

Installing the plugin

• Ionic

ionic cordova plugin add cordova-plugin-background-fetch

• Pure Cordova

cordova plugin add cordova-plugin-background-fetch

• Capacitor

npm install cordova-plugin-background-fetch
npx cap sync

ℹ️ See Capacitor Setup

• PhoneGap Build

  <plugin name="cordova-plugin-background-fetch" source="npm" />

iOS Setup [:new: iOS 13+]

If you intend to execute your own custom tasks via BackgroundFetch.scheduleTask, for example:

BackgroundFetch.scheduleTask({
  taskId: 'com.transistorsoft.customtask1',  // <-- Your custom task-identifier
  delay: 60 * 60 * 1000  //  In one hour (milliseconds)
});
.
.
.
BackgroundFetch.scheduleTask({
  taskId: 'com.transistorsoft.customtask2',  // <-- Your custom task-identifier
  delay: 60 * 60 * 1000  //  In one hour (milliseconds)
});

You must register these custom task-identifiers with your iOS app's Info.plist "Permitted background task scheduler identifiers":

📂 In your config.xml, find the <platform name="ios"> container and register your custom task-identifier(s):

  <platform name="ios">
      <config-file parent="BGTaskSchedulerPermittedIdentifiers" target="*-Info.plist">
          <array>
              <string>com.transistorsoft.customtask1</string>
              <string>com.transistorsoft.customtask2</string>
          </array>
      </config-file>
  </platform>

⚠️ A task identifier can be any string you wish, but it's a good idea to prefix them now with com.transistorsoft. — In the future, the com.transistorsoft prefix may become required.

Example

Pure Cordova Javascript (eg: Ionic 1)

onDeviceReady: function() {
  var BackgroundFetch = window.BackgroundFetch;

  // Your background-fetch handler.
  var fetchCallback = function(taskId) {
    console.log('[js] BackgroundFetch event received: ', taskId);
    // Required: Signal completion of your task to native code
    // If you fail to do this, the OS can terminate your app
    // or assign battery-blame for consuming too much background-time
    BackgroundFetch.finish(taskId);
  };

  var failureCallback = function(error) {
    console.log('- BackgroundFetch failed', error);
  };

  BackgroundFetch.configure(fetchCallback, failureCallback, {
    minimumFetchInterval: 15 // <-- default is 15
  });
}

Ionic 2+ Example

import { Component } from '@angular/core';
import { NavController, Platform } from 'ionic-angular';

import BackgroundFetch from "cordova-plugin-background-fetch";

@Component({
  selector: 'page-home',
  templateUrl: 'home.html'
})
export class HomePage {
  constructor(public navCtrl: NavController, public platform: Platform) {
    this.platform.ready().then(this.onDeviceReady.bind(this));
  }

  onDeviceReady() {
    // Your background-fetch handler.
    let fetchCallback = function(taskId) {
        console.log('[js] BackgroundFetch event received: ', taskId);
        // Required: Signal completion of your task to native code
        // If you fail to do this, the OS can terminate your app
        // or assign battery-blame for consuming too much background-time
        BackgroundFetch.finish(taskId);
    };

    let failureCallback = function(error) {
        console.log('- BackgroundFetch failed', error);
    };

    BackgroundFetch.configure(fetchCallback, failureCallback, {
        minimumFetchInterval: 15 // <-- default is 15
    });
  }
}

Executing Custom Tasks

In addition to the default background-fetch task defined by BackgroundFetch.configure, you may also execute your own arbitrary "oneshot" or periodic tasks (iOS requires additional Setup Instructions). However, all events will be fired into the Callback provided to BackgroundFetch#configure:

⚠️ iOS: Custom iOS tasks seem only to run while device is plugged into power. Hopefully Apple changes this in the future.

// Step 1:  Configure BackgroundFetch as usual.
BackgroundFetch.configure({
  minimumFetchInterval: 15
), (taskId) => {
  // This is the fetch-event callback.
  console.log("[BackgroundFetch] taskId: ", taskId);

  // Use a switch statement to route task-handling.
  switch (taskId) {
    case 'com.transistorsoft.customtask':
      print("Received custom task");
      break;
    default:
      print("Default fetch task");
  }
  // Finish, providing received taskId.
  BackgroundFetch.finish(taskId);
});

// Step 2:  Schedule a custom "oneshot" task "com.transistorsoft.customtask" to execute 5000ms from now.
BackgroundFetch.scheduleTask({
  taskId: "com.transistorsoft.customtask",
  forceAlarmManager: true,
  delay: 5000  // <-- milliseconds
});

Config

Common Options

@param {Integer} minimumFetchInterval [15]

The minimum interval in minutes to execute background fetch events. Defaults to 15 minutes. Note: Background-fetch events will never occur at a frequency higher than every 15 minutes. Apple uses a secret algorithm to adjust the frequency of fetch events, presumably based upon usage patterns of the app. Fetch events can occur less often than your configured minimumFetchInterval.

@param {Integer} delay (milliseconds)

ℹ️ Valid only for BackgroundGeolocation.scheduleTask. The minimum number of milliseconds in future that task should execute.

@param {Boolean} periodic [false]

ℹ️ Valid only for BackgroundGeolocation.scheduleTask. Defaults to false. Set true to execute the task repeatedly. When false, the task will execute just once.

Android Options

@config {Boolean} stopOnTerminate [true]

Set false to continue background-fetch events after user terminates the app. Default to true.

@config {Boolean} startOnBoot [false]

Set true to initiate background-fetch events when the device is rebooted. Defaults to false.

❗ NOTE: startOnBoot requires stopOnTerminate: false.

@config {Boolean} forceAlarmManager [false]

By default, the plugin will use Android's JobScheduler when possible. The JobScheduler API prioritizes for battery-life, throttling task-execution based upon device usage and battery level.

Configuring forceAlarmManager: true will bypass JobScheduler to use Android's older AlarmManager API, resulting in more accurate task-execution at the cost of higher battery usage.

BackgroundFetch.configure({
  minimumFetchInterval: 15,
  forceAlarmManager: true
}, async (taskId) => {
  console.log("[BackgroundFetch] taskId: ", taskId);
  BackgroundFetch.finish(taskId);
});
.
.
.
// And with with #scheduleTask
BackgroundFetch.scheduleTask({
  taskId: 'com.transistorsoft.customtask',
  delay: 5000,       // milliseconds
  forceAlarmManager: true
  periodic: false
});

@config {integer} requiredNetworkType [BackgroundFetch.NETWORK_TYPE_NONE]

Set basic description of the kind of network your job requires.

If your job doesn't need a network connection, you don't need use this options as the default value is BackgroundFetch.NETWORK_TYPE_NONE.

NetworkType	Description
BackgroundFetch.NETWORK_TYPE_NONE	This job doesn't care about network constraints, either any or none.
BackgroundFetch.NETWORK_TYPE_ANY	This job requires network connectivity.
BackgroundFetch.NETWORK_TYPE_CELLULAR	This job requires network connectivity that is a cellular network.
BackgroundFetch.NETWORK_TYPE_UNMETERED	This job requires network connectivity that is unmetered.
BackgroundFetch.NETWORK_TYPE_NOT_ROAMING	This job requires network connectivity that is not roaming.

@config {Boolean} requiresBatteryNotLow [false]

Specify that to run this job, the device's battery level must not be low.

This defaults to false. If true, the job will only run when the battery level is not low, which is generally the point where the user is given a "low battery" warning.

@config {Boolean} requiresStorageNotLow [false]

Specify that to run this job, the device's available storage must not be low.

This defaults to false. If true, the job will only run when the device is not in a low storage state, which is generally the point where the user is given a "low storage" warning.

@config {Boolean} requiresCharging [false]

Specify that to run this job, the device must be charging (or be a non-battery-powered device connected to permanent power, such as Android TV devices). This defaults to false.

@config {Boolean} requiresDeviceIdle [false]

When set true, ensure that this job will not run if the device is in active use.

The default state is false: that is, the for the job to be runnable even when someone is interacting with the device.

This state is a loose definition provided by the system. In general, it means that the device is not currently being used interactively, and has not been in use for some time. As such, it is a good time to perform resource heavy jobs. Bear in mind that battery usage will still be attributed to your application, and surfaced to the user in battery stats.

@config {Boolean} enableHeadless [false]

⚠️ For advanced users only. In order to use enableHeadless: true, you must be prepared to write Java code. If you're not prepared to write Java code, turn away now and do not enable this ⚠️.

When your application is terminated with stopOnTerminate: false, your Javascript app (and your Javascript fetch callback) are terminated. However, the plugin provides a mechanism for you to handle background-fetch events in the Native Android Environment.

Some examples where you could use the "Headless" mechanism:

• Refreshing API keys.
• Performing HTTP requests with your server.
• Posting a local notification

Headless Fetch Setup

1. create a new file in your Cordova application named BackgroundFetchHeadlessTask.java. ⚠️ The file can be located anywhere in your app but MUST be named BackgroundFetchHeadlessTask.java.

eg: 📂 src/android/BackgroundFetchHeadlessTask.java

package com.transistorsoft.cordova.backgroundfetch;
import android.content.Context;
import com.transistorsoft.tsbackgroundfetch.BackgroundFetch;
import android.util.Log;

public class BackgroundFetchHeadlessTask implements HeadlessTask {
    @Override
    public void onFetch(Context context, String taskId) {
        Log.d(BackgroundFetch.TAG, "My BackgroundFetchHeadlessTask:  onFetch: " + taskId);
        // Perform your work here.

        // Just as in Javascript callback, you must signal #finish
        BackgroundFetch.getInstance(context).finish(taskId);
    }
}

2. In your config.xml, add the following <resource-file> element to the <platform name="android">:

<platform name="android">
    <resource-file src="src/android/BackgroundFetchHeadlessTask.java" target="app/src/main/java/com/transistorsoft/cordova/backgroundfetch/BackgroundFetchHeadlessTask.java" />
</platform>

• src: path to your custom BackgroundFetchHeadlessTask.java file.
• target: ⚠️ Must be exactly as shown above.

This will copy your custom Java source-file into the cordova-plugin-background-fetch plugin, effectively overriding the plugin.

⚠️ You're responsible for managing your own gradle dependencies. To import 3rd-party libraries, you'll have to import your own custom build-extras.gradle (See "build-extras" here in the Cordova Android Platform Documentation)

Methods

Method Name	Arguments	Notes
configure	callbackFn, failureFn, {BackgroundFetchConfig}	Configures the plugin's fetch callbackFn. This callback will fire each time an iOS background-fetch event occurs (typically every 15 min). The failureFn will be called if the device doesn't support background-fetch.
scheduleTask	{TaskConfig}	Executes a custom task. The task will be executed in the same Callback function provided to #configure.
stopTask	String taskId, successFn,failureFn	Stops a scheduleTask from running.
finish	String taskId	You MUST call this method in your callbackFn provided to #configure in order to signal to the OS that your task is complete. iOS provides only 30s of background-time for a fetch-event -- if you exceed this 30s, iOS will kill your app.
start	successFn, failureFn	Start the background-fetch API. Your callbackFn provided to #configure will be executed each time a background-fetch event occurs. NOTE the #configure method automatically calls #start. You do not have to call this method after you #configure the plugin
stop	successFn, failureFn	Stop the background-fetch API from firing fetch events. Your callbackFn provided to #configure will no longer be executed.
status	callbackFn	Your callback will be executed with the current status (Integer) 0: Restricted, 1: Denied, 2: Available. These constants are defined as BackgroundFetch.STATUS_RESTRICTED, BackgroundFetch.STATUS_DENIED, BackgroundFetch.STATUS_AVAILABLE (NOTE: Android will always return STATUS_AVAILABLE)

Debugging

iOS

🆕 BGTaskScheduler API for iOS 13+

• ⚠️ At the time of writing, the new task simulator does not yet work in Simulator; Only real devices.
• See Apple docs Starting and Terminating Tasks During Development
• After running your app in XCode, Click the [||] button to initiate a Breakpoint.
• In the console (lldb), paste the following command (Note: use cursor up/down keys to cycle through previously run commands):

e -l objc -- (void)[[BGTaskScheduler sharedScheduler] _simulateLaunchForTaskWithIdentifier:@"com.transistorsoft.fetch"]

• Click the [ > ] button to continue. The task will execute and the Callback function provided to BackgroundFetch.configure will receive the event.

Old BackgroundFetch API

• Simulate background fetch events in XCode using Debug->Simulate Background Fetch
• iOS can take some hours or even days to start a consistently scheduling background-fetch events since iOS schedules fetch events based upon the user's patterns of activity. If Simulate Background Fetch works, your can be sure that everything is working fine. You just need to wait.

Android

• Observe plugin logs in $ adb logcat:

$ adb logcat -s TSBackgroundFetch

• Simulate a background-fetch event on a device (insert <your.application.id>) (only works for sdk 24+):

$ adb shell cmd jobscheduler run -f <your.application.id> 999

• For devices with sdk <21, simulate a "Headless JS" event with (insert <your.application.id>)

$ adb shell am broadcast -a <your.application.id>.event.BACKGROUND_FETCH

iOS

Implements BGTaskScheduler for devices running iOS 13+ in addition to performFetchWithCompletionHandler for devices <iOS 13, firing a custom event subscribed-to in cordova plugin. Unfortunately, iOS automatically ceases background-fetch events when the user explicitly terminates the application or reboots the device.

Android

Android implements background fetch using two different mechanisms, depending on the Android SDK version. Where the SDK version is >= LOLLIPOP, the new JobScheduler API is used. Otherwise, the old AlarmManager will be used.

Unlike iOS, the Android implementation can continue to operate after application terminate (stopOnTerminate: false) or device reboot (startOnBoot: true).

Licence

The MIT License

Copyright (c) 2018 Chris Scott, Transistor Software [email protected] http://transistorsoft.com

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.