Expo Docs MCP Server

--- title: BackgroundFetch description: A library that provides API for performing background fetch tasks. sourceCodeUrl: https://github.com/expo/expo/tree/main/packages/expo-background-fetch packageName: expo-background-fetch platforms: ["android", "ios"] isDeprecated: true --- > **warning** **Deprecated:** The `expo-background-fetch` library is being replaced by a new version in [`expo-background-task`](background-task.md). `expo-background-fetch` is not receiving patches and will be removed in an upcoming release. `expo-background-fetch` provides an API to perform [background fetch](https://developer.apple.com/documentation/uikit/core_app/managing_your_app_s_life_cycle/preparing_your_app_to_run_in_the_background/updating_your_app_with_background_app_refresh) tasks, allowing you to run specific code periodically in the background to update your app. This module uses [TaskManager](task-manager.md) Native API under the hood. #### Known issues&ensp; `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](https://github.com/expo/expo/issues/3582) for more details. On iOS the `BackgroundFetch` library requires you to use a [development build](/develop/development-builds/introduction/) since Background Fetch is not enabled in the iOS Expo Go app. ## Installation ## Configuration&ensp; 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](/workflow/continuous-native-generation/)**, the required `UIBackgroundModes` configuration will be applied automatically by prebuild. If you're not using Continuous Native Generation ([CNG](/workflow/continuous-native-generation/)) or you're using a native **ios** project manually, then you'll need to add the following to your **Expo.plist** file: ```xml 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`. ```tsx 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); } const [isRegistered, setIsRegistered] = useState(false); const [status, setStatus] = useState(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> </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 (⌘ + 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: ```tsx async function registerBackgroundFetchAsync() { return BackgroundFetch.registerTaskAsync(BACKGROUND_FETCH_TASK, { minimumInterval: 1 * 60, // task will fire 1 minute after app is backgrounded }); } ``` ## API ```js ``` ## 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.