IOS background fetch never runs

Expo SDK
1

Please provide the following:

  1. SDK Version: 40
  2. Platforms: iOS
  3. Managed App not ejected.

I have been trying to get Background Fetch on iOS for a few weeks now but with no luck. I followed the steps in the docs correctly but have been unable to get it to run on iOS. I am including a snippet of my code below, if anyone could point out my issue it would be greatly appreciated.

startBackgroundTask below is called from the global scope in app.js

  const startBackgroundTask = async () => {
    TaskManager.defineTask(BACKGROUND_FETCH_TASK, async () => {
      console.log('BackgroundTask running');
      try {
        // I am making a console.log and then calling an API here
        return BackgroundFetch.Result.NewData;
      } catch (err) {
        console.log(`Error occured while running task: ${err.message}`, err);
        return BackgroundFetch.Result.Failed;
      }
    });

    const status = await BackgroundFetch.getStatusAsync();

    if (status === BackgroundFetch.Status.Restricted || status === BackgroundFetch.Status.Denied) {
      console.log('Background fetch is disabled.');
      return;
    }

    try {
      await BackgroundFetch.registerTaskAsync(BACKGROUND_FETCH_TASK, {
        minimumInterval: INTERVAL,
        stopOnTerminate: true,
        startOnBoot: false,
      });
      await BackgroundFetch.setMinimumIntervalAsync(INTERVAL);
      console.log('Background update task registered.');
    } catch (err) {
      console.log('Filed to register task for background.', err);
    }
  }

Result:
Console.log never prints and the task is never executed.

1 Like
2

Hey @khsrikanth, could you create a minimal new project with the code and configuration you’ve implemented so that I can clone and test on my end?

Cheers,
Adam

3

Hi Adam,

So yesterday I tried cloning the expo example apps repo:

It has a BackgroundFetchScreen that has what I need and I was not able to get it to work either. the screen always stays at “There was no BackgroundFetch call yet.”

4

@adamjnav Please could you clone the expo repo and see if the background fetch in the example works for you?

5

I want to add my minimal example. trajano/expo-mvce (github.com) it also works on Android Expo client but not iOS. expo client:ios

iOS 14.4

@khsrikanth can you try my MVCE as well? It’s based off the one from the component list but I added more debugging.

There’s a github issue on this as well [expo-background-fetch] Background fetch is not running · Issue #9900 · expo/expo (github.com)

6

I tried to do an expo build:ios for simulator but the experiment doesn’t even show notifications when I drag and drop the app into the simulator. The permissions dialog does not show up while on managed

I did a few other experiments one of them is to eject the app. This made the notifications work again. But the background task still does not fire.

However, the weird part is sometimes at random times during the day it does get “triggered” the thing is I can’t find a proper pattern. I know its not supposed to be predictable to the second but I can’t even tell the frequency per hour is more than 0.

I found a 5 year old Stack Overflow article about this behaviour ios7 - How often is background fetch executed in iOS? - Stack Overflow but it just says it’s not known.

7

Awesome @trajano!!! Thank you for your reply. I will definitely try the example out. Were you able to trigger a local notification from the background fetch?

8

In the end. yes. But as I noted in the last part, it is very unpredictable. The best way to guarantee it runs is if the phone is plugged in.

You’d also notice the same behaviour with other apps that have Background Fetch but no push notifications.

9

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