Trying to use BGAppRefreshTask and getting error No task request with identifier <decode: missing data> has been scheduled

Question

I kept getting the error

No task request with identifier <decode: missing data> has been scheduled

in my debugger output so I decided to try running the example code provided by Apple here and got the same error. I've tried multiple computers and Xcode versions, multiple example projects from different sources and nothing has worked.

My AppDelegate.swift file:

import UIKit
import Firebase
import BackgroundTasks

@main
class AppDelegate: UIResponder, UIApplicationDelegate {
    
    func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
        
        FirebaseApp.configure()
                
        BGTaskScheduler.shared.register(forTaskWithIdentifier: “redacted.identifier”, using: nil) { task in
            self.handleAppRefresh(task: task as! BGAppRefreshTask)
        }
        
        return true
    }
    
    func applicationDidEnterBackground(_ application: UIApplication) {
        BGTaskScheduler.shared.cancelAllTaskRequests()
        scheduleAppRefresh()
    }
    
     func scheduleAppRefresh() {
        let request = BGAppRefreshTaskRequest(identifier: "redacted.identifier")
        
        request.earliestBeginDate = Date(timeIntervalSinceNow: 60)
        do {
            try BGTaskScheduler.shared.submit(request)
        } catch {
            print("Could not schedule app refresh: \(error)")
        }
    }
    
    func handleAppRefresh(task: BGAppRefreshTask) {
        scheduleAppRefresh()
        
        let db = Firestore.firestore()
        
        db.collection("devices").document(UIDevice.current.identifierForVendor!.uuidString).setData([
            "batteryLevel": UIDevice.current.batteryLevel*100
            ]) { err in
            if let err = err {
                print("Error writing document: \(err)")
            } else {
                print("success")
                task.setTaskCompleted(success: true)
            }
        }
        
        task.expirationHandler = {
            task.setTaskCompleted(success: false)
        }
    }

I am testing background fetch by running

e -l objc -- (void)[[BGTaskScheduler sharedScheduler] _simulateLaunchForTaskWithIdentifier:@"redacted.identifier"]

in the Xcode console, after which the error above occurs.

Console output:

Simulating launch for task with identifier redacted.identifier

No task request with identifier <decode: missing data> has been scheduled

Answer 1

A couple of potential issues:

• This happens when testing on the simulator. Use a physical device.

• Make sure your Info.plist has a “Permitted background task scheduler identifiers” (i.e. BGTaskSchedulerPermittedIdentifiers) entry with the identifier for your background task.

• Make sure you set your breakpoint immediately after the BGTaskScheduler.shared.submit(...) line and that you perform the _simulateLaunchForTaskWithIdentifier after submit was called. I.e., make sure you are even getting to the submit call. (See next point.)

• Notably, the Apple example (and your example) are scheduling it in applicationDidEnterBackground(_:). But if you are using a UIWindowSceneDelegate (i.e. in your SceneDelegate), then the app delegate’s applicationDidEnterBackground(_:) is not called, but rather the scene delegate’s sceneDidEnterBackground(_:) is. I put the scheduling of the BGAppRefreshTaskRequest in the scene delegate’s sceneDidEnterBackground(_:).