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.

Using the plugin

The plugin creates the object window.BackgroundFetch.

Installing the plugin

Command Line

   $ cordova plugin add cordova-plugin-background-fetch

PhoneGap Build

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

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.

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} forceReload [false]`

Set true to automatically relaunch the application (if it was terminated) — the application will launch to the foreground then immediately minimize. Defaults to false.

`@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, as an alternative to forceReload: true, which forcibly re-launches your entire Cordova application.

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

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) {
        Log.d(BackgroundFetch.TAG, "My BackgroundFetchHeadlessTask:  onFetch");
        // Perform your work here.

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

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="src/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`, `{config}`	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.
`finish`	none	You MUST call this method in your fetch `callbackFn` provided to `#configure` in order to signal to iOS that your fetch action 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.

Example

Pure Cordova Javascript (eg: Ionic 1)

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

  // Your background-fetch handler.
  var fetchCallback = function() {
    console.log('[js] BackgroundFetch event received');

    // 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();
  };

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

  BackgroundFetch.configure(fetchCallback, failureCallback, {
    minimumFetchInterval: 15, // <-- default is 15
    stopOnTerminate: false,   // <-- Android only
    startOnBoot: true,        // <-- Android only
    forceReload: true         // <-- Android only
  });
}

Ionic 2+ Example

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

@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() {
    let BackgroundFetch = (<any>window).BackgroundFetch;
        
    // Your background-fetch handler.
    let fetchCallback = function() {
        console.log('[js] BackgroundFetch event received');
        // 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();
    }
    let failureCallback = function(error) {
        console.log('- BackgroundFetch failed', error);
    };
    BackgroundFetch.configure(fetchCallback, failureCallback, {
        minimumFetchInterval: 15, // <-- default is 15
        stopOnTerminate: false,   // <-- Android only
        startOnBoot: true,        // <-- Android only
        forceReload: true         // <-- Android only
    });        
  }
}

Debugging

iOS

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 performFetchWithCompletionHandler, 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

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.

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