react-native-background-task
Periodic background tasks for React Native apps, cross-platform (iOS and Android), which run even when the app is closed.
This library allows the scheduling of a single periodic task, which executes when the app is in the background or closed, no more frequently than every 15 minutes. Network, AsyncStorage etc can be used (anything except UI), so perfect for things like a background data sync for offline support.
Behind the scenes, this library takes a different approach with each platform:
- Android: A native implementation, which provides scheduling on top of
- iOS: A proxy around react-native-background-fetch,
Background Fetch
technique.To achieve a unified API, this library exposes the lowest common denominator (e.g. only support for a single task, even though Android can support multiple).
For more per-platform flexibility, there are other platform-specific libraries with more granular customisation.
Installation
$ npm install react-native-background-task --save
Android
- The linking of the library can be done automatically by running:
```bash $ react-native link react-native-background-task ```
- One manual step is still needed - in your project file
android/app/src/main/java/myapp/MainApplication.java
, add the following to
the end of the onCreate()
method:
```java BackgroundTaskPackage.useContext(this); ```
iOS
For iOS support, this library relies on version 2.0.x of react-native-background-fetch which can be installed as follows:$ npm install react-native-background-fetch@2.0.x --save
$ react-native link react-native-background-fetch
This library will behave correctly on iOS as long as
react-native-background-fetch
is installed alongside it, and has been linked with your project.API
define(task)
Define the JS code that this module should be executing.- Should be called at the top level of your JS, not inside a component.
- Will overwrite any previously defined task.
Parameters:
task
: required() => void
- Function to be executed in the background
schedule(options)
Specify the scheduling options for the task, and register it with the
platform's scheduler.- Should be called from inside a component (e.g. your App's
componentDidMount
). This is to avoid double-scheduling when the task
launches in headless mode.- Will
console.warn
if the device is task was unable to be scheduled.
Parameters:
options?
:Object
- Any configuration you want to be set with
-
period?
: number
- (Android only) Desired number of seconds between eachexecution of the task. Even on Android, the OS will only take this as a
recommendation, and will enforce a minimum of 15 minutes (similar to iOS).
Default is 900 (15 minutes)
- timeout?
: number
- (Android only) Number of seconds the task will haveto execute. iOS has a hardcoded limit of 30 seconds. Default 30 seconds.
finish()
Must be called at the end of your task to indicate to the OS that it's
finished. (Only required on iOS, no-op on Android).cancel()
Cancels any currently scheduled task.statusAsync()
Query the status of background tasks within this app. Returns a Promise with
an object of the following shape:available
:boolean
- Whether background tasks are available to the app.
unavailableReason?
:string
- If unavailable, gives the reason:
- **`BackgroundTask.UNAVAILABLE_DENIED`**: - The user explicitly disabled
background behavior for this app or for the whole system.
- **`BackgroundTask.UNAVAILABLE_RESTRICTED`**: - Background updates
unavailable and can't be enabled by the user (e.g. parental controls).
Limitations
- Tasks cannot be scheduled any more frequently than every 15 minutes.
- The exact timings of task execution are unpredictable, as both Anrdoid and
Android:
- Tasks will not run while the app is in the foreground, and scheduling can be
iOS:
- iOS Background Fetch will not continue to run after a user manually closes
- Background tasks will not be scheduled in the simulator. You'll need to
- The user can disable Background App Refresh for your app from their Settings
statusAsync()
to check for this).Debugging
Android
$ adb logcat *:S ReactNative:V ReactNativeJS:V BackgroundTask:V
Keep in mind that after the app leaves the foreground, you'll have to wait at least 50% of the desired period (so, default is 7m30s) before the task executes.
Examples
Simple
import React from 'react'
import { Text } from 'react-native'
import BackgroundTask from 'react-native-background-task'
BackgroundTask.define(() => {
console.log('Hello from a background task')
BackgroundTask.finish()
})
class MyApp extends React.Component {
componentDidMount() {
BackgroundTask.schedule()
}
render() {
return <Text>Hello world</Text>
}
}
Fetch / store data
import React from 'react'
import { Alert, AsyncStorage, Button } from 'react-native'
import BackgroundTask from 'react-native-background-task'
BackgroundTask.define(async () => {
// Fetch some data over the network which we want the user to have an up-to-
// date copy of, even if they have no network when using the app
const response = await fetch('http://feeds.bbci.co.uk/news/rss.xml')
const text = await response.text()
// Data persisted to AsyncStorage can later be accessed by the foreground app
await AsyncStorage.setItem('@MyApp:key', text)
// Remember to call finish()
BackgroundTask.finish()
})
class MyApp extends React.Component {
componentDidMount() {
BackgroundTask.schedule({
period: 1800, // Aim to run every 30 mins - more conservative on battery
})
// Optional: Check if the device is blocking background tasks or not
this.checkStatus()
}
async checkStatus() {
const status = await BackgroundTask.statusAsync()
if (status.available) {
// Everything's fine
return
}
const reason = status.unavailableReason
if (reason === BackgroundTask.UNAVAILABLE_DENIED) {
Alert.alert('Denied', 'Please enable background "Background App Refresh" for this app')
} else if (reason === BackgroundTask.UNAVAILABLE_RESTRICTED) {
Alert.alert('Restricted', 'Background tasks are restricted on your device')
}
}
render() {
return (
<View>
<Button
title="Read results from AsyncStorage"
onPress={async () => {
const result = await AsyncStorage.getItem('@MyApp:key')
console.log(result)
}}
/>
</View>
)
}
}