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Expo BackgroundFetch

A library that provides API for performing background fetch tasks.

Android
iOS
Recommended version:
~56.0.27

expo-background-fetch provides an API to perform background fetch tasks, allowing you to run specific code periodically in the background to update your app. This module uses TaskManager Native API under the hood.

Known issues 
iOS

BackgroundFetch only works when the app is backgrounded, not if the app was terminated or upon device reboot. You can check out the relevant GitHub issue for more details.

On iOS the BackgroundFetch library requires you to use a development build since Background Fetch is not enabled in the iOS Expo Go app.

Installation

Terminal
- npx expo install expo-background-fetch
- yarn expo install expo-background-fetch
- pnpm expo install expo-background-fetch
- bun expo install expo-background-fetch

If you are installing this in an existing React Native app, make sure to install expo in your project.

Configuration 
iOS

To be able to run background fetch tasks on iOS, you need to add the fetch value to the UIBackgroundModes array in your app's Info.plist file. This is required for background fetch to work properly.

If you're using CNG, the required UIBackgroundModes configuration will be applied automatically by prebuild.

Configure UIBackgroundModes manually on iOS

If you're not using Continuous Native Generation (CNG) or you're using a native ios project manually, then you'll need to add the following to your Expo.plist file:

ios/project-name/Supporting/Expo.plist
<key>UIBackgroundModes</key> <array> <string>fetch</string> </array>

Usage

Below is an example that demonstrates how to use expo-background-fetch.

Background Fetch Usage
import { useState, useEffect } from 'react'; import { StyleSheet, Text, View, Button } from 'react-native'; import * as BackgroundFetch from 'expo-background-fetch'; import * as TaskManager from 'expo-task-manager'; const BACKGROUND_FETCH_TASK = 'background-fetch'; // 1. Define the task by providing a name and the function that should be executed // Note: This needs to be called in the global scope (e.g outside of your React components) TaskManager.defineTask(BACKGROUND_FETCH_TASK, async () => { const now = Date.now(); console.log(`Got background fetch call at date: ${new Date(now).toISOString()}`); // Be sure to return the successful result type! return BackgroundFetch.BackgroundFetchResult.NewData; }); // 2. Register the task at some point in your app by providing the same name, // and some configuration options for how the background fetch should behave // Note: This does NOT need to be in the global scope and CAN be used in your React components! async function registerBackgroundFetchAsync() { return BackgroundFetch.registerTaskAsync(BACKGROUND_FETCH_TASK, { minimumInterval: 60 * 15, // 15 minutes stopOnTerminate: false, // android only, startOnBoot: true, // android only }); } // 3. (Optional) Unregister tasks by specifying the task name // This will cancel any future background fetch calls that match the given name // Note: This does NOT need to be in the global scope and CAN be used in your React components! async function unregisterBackgroundFetchAsync() { return BackgroundFetch.unregisterTaskAsync(BACKGROUND_FETCH_TASK); } export default function BackgroundFetchScreen() { const [isRegistered, setIsRegistered] = useState(false); const [status, setStatus] = useState<BackgroundFetch.BackgroundFetchStatus | null>(null); useEffect(() => { checkStatusAsync(); }, []); const checkStatusAsync = async () => { const status = await BackgroundFetch.getStatusAsync(); const isRegistered = await TaskManager.isTaskRegisteredAsync(BACKGROUND_FETCH_TASK); setStatus(status); setIsRegistered(isRegistered); }; const toggleFetchTask = async () => { if (isRegistered) { await unregisterBackgroundFetchAsync(); } else { await registerBackgroundFetchAsync(); } checkStatusAsync(); }; return ( <View style={styles.screen}> <View style={styles.textContainer}> <Text> Background fetch status:{' '} <Text style={styles.boldText}> {status && BackgroundFetch.BackgroundFetchStatus[status]} </Text> </Text> <Text> Background fetch task name:{' '} <Text style={styles.boldText}> {isRegistered ? BACKGROUND_FETCH_TASK : 'Not registered yet!'} </Text> </Text> </View> <View style={styles.textContainer}></View> <Button title={isRegistered ? 'Unregister BackgroundFetch task' : 'Register BackgroundFetch task'} onPress={toggleFetchTask} /> </View> ); } const styles = StyleSheet.create({ screen: { flex: 1, justifyContent: 'center', alignItems: 'center', }, textContainer: { margin: 10, }, boldText: { fontWeight: 'bold', }, });

Triggering background fetches

Background fetches can be difficult to test because they can happen inconsistently. Fortunately, you can trigger background fetches manually when developing your apps.

For iOS, you can use the Instruments app on macOS to manually trigger background fetches:

  1. Open the Instruments app. The Instruments app can be searched through Spotlight (Cmd ⌘ + Space) or opened from /Applications/Xcode.app/Contents/Applications/Instruments.app
  2. Select Time Profiler
  3. Select your device / simulator and pick the Expo Go app
  4. Press the Record button in the top left corner
  5. Navigate to the Document Menu and select Simulate Background Fetch - Expo Go:

For Android, you can set the minimumInterval option of your task to a small number and background your application like so:

async function registerBackgroundFetchAsync() { return BackgroundFetch.registerTaskAsync(BACKGROUND_FETCH_TASK, { minimumInterval: 1 * 60, // task will fire 1 minute after app is backgrounded }); }

API

import * as BackgroundFetch from 'expo-background-fetch';

No API data file found, sorry!

Permissions

Android

On Android, this module might listen when the device is starting up. It's necessary to continue working on tasks started with startOnBoot. It also keeps devices "awake" that are going idle and asleep fast, to improve reliability of the tasks. Because of this both the RECEIVE_BOOT_COMPLETED and WAKE_LOCK permissions are added automatically.

Android permissionDescription

RECEIVE_BOOT_COMPLETED

Allows an application to receive the Intent.ACTION_BOOT_COMPLETED that is broadcast after the system finishes booting.

WAKE_LOCK

Allows using PowerManager WakeLocks to keep processor from sleeping or screen from dimming.