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transistorsoft / capacitor-background-fetch

Periodic callbacks in the background for both IOS and Android
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@transistorsoft/capacitor-background-fetch

By Transistor Software, creators of Capacitor Background Geolocation

Background Fetch is a very simple plugin which attempts to 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 or if an iOS user disables background refresh they may not happen at all.

:rotating_light: This plugin requires Capacitor 5 :rotating_light:

For Capacitor 4, use the 1.x version of the plugin.

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

iOS

Android

Contents

Installing the plugin

With yarn

$ yarn add @transistorsoft/capacitor-background-fetch
$ npx cap sync

With npm

$ npm install --save @transistorsoft/capacitor-background-fetch
$ npx cap sync

Setup Guides

iOS Setup

Android Setup

Example

:information_source: This repo contains its own Example App. See /example

Angular Example:

import { Component } from '@angular/core';

import {BackgroundFetch} from '@transistorsoft/capacitor-background-fetch';

@Component({
  selector: 'app-home',
  templateUrl: 'home.page.html',
  styleUrls: ['home.page.scss'],
})
export class HomePage {
  constructor() {}

  // Initialize in ngAfterContentInit
  // [WARNING] DO NOT use ionViewWillEnter, as that method won't run when app is launched in background.
  ngAfterContentInit() {
    this.initBackgroundFetch();
  }

  async initBackgroundFetch() {
    const status = await BackgroundFetch.configure({
      minimumFetchInterval: 15
    }, async (taskId) => {
      console.log('[BackgroundFetch] EVENT:', taskId);
      // Perform your work in an awaited Promise
      const result = await this.performYourWorkHere();
      console.log('[BackgroundFetch] work complete:', result);
      // [REQUIRED] Signal to the OS that your work is complete.
      BackgroundFetch.finish(taskId);
    }, async (taskId) => {
      // The OS has signalled that your remaining background-time has expired.
      // You must immediately complete your work and signal #finish.
      console.log('[BackgroundFetch] TIMEOUT:', taskId);
      // [REQUIRED] Signal to the OS that your work is complete.
      BackgroundFetch.finish(taskId);
    });

    // Checking BackgroundFetch status:
    if (status !== BackgroundFetch.STATUS_AVAILABLE) {
      // Uh-oh:  we have a problem:
      if (status === BackgroundFetch.STATUS_DENIED) {
        alert('The user explicitly disabled background behavior for this app or for the whole system.');
      } else if (status === BackgroundFetch.STATUS_RESTRICTED) {
        alert('Background updates are unavailable and the user cannot enable them again.')
      }
    }
  }

  async performYourWorkHere() {
    return new Promise((resolve, reject) => {
      setTimeout(() => {
        resolve(true);
      }, 5000);
    });
  }
}

Receiving Events After App Termination

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). See API Docs BackgroundFetch.scheduleTask. However, all events will be fired into the Callback provided to BackgroundFetch.configure.

⚠️ iOS:

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

  // Use a switch statement to route task-handling.
  switch (taskId) {
    case 'com.foo.customtask':
      print("Received custom task");
      break;
    default:
      print("Default fetch task");
  }
  // Finish, providing received taskId.
  BackgroundFetch.finish(taskId);
}, async (taskId) => {  // <-- Task timeout callback
  // This task has exceeded its allowed running-time.
  // You must stop what you're doing and immediately .finish(taskId)
  BackgroundFetch.finish(taskId);
});

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

Debugging

iOS Simulated Events

:new: BGTaskScheduler API for iOS 13+

Simulating task-timeout events

const status = await BackgroundFetch.configure({
  minimumFetchInterval: 15
}, async (taskId) => {  // <-- Event callback.
  // This is the task callback.
  console.log("[BackgroundFetch] taskId", taskId);
  //BackgroundFetch.finish(taskId); // <-- Disable .finish(taskId) when simulating an iOS task timeout
}, async (taskId) => {  // <-- Event timeout callback
  // This task has exceeded its allowed running-time.
  // You must stop what you're doing and immediately .finish(taskId)
  console.log("[BackgroundFetch] TIMEOUT taskId:", taskId);
  BackgroundFetch.finish(taskId);
});

Old BackgroundFetch API

Android Simulated Events

$ adb logcat *:S TSBackgroundFetch:V Capacitor/Console:V Capacitor/Plugin:V


## Licence

The MIT License

Copyright (c) 2013 Chris Scott, Transistor Software <chris@transistorsoft.com>
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.