onBackgroundData not called

I circumvented this whole system by just using Storage and onStorageChanged.  It works for me, and perhaps it can work for you as a workaround?  Pick a key.  Clear it when you start the background (as double confirmation).  Set it when you're exiting.  Listen for that on the front-end code. If non-null, act on it and clear storage for that key for next time.  

(This isn't exactly how I do it -- this seems wasteful if you're just trying to message-pass.  In my actual use case, I do require the information to be stored anyway, so it's not wasteful.  But it could create a simple message-passing system, too).

Yeah, I also found onStorageChanged yesterday, and thought that maybe I'll use it instead.

"Since API Level 3.2.0"

I still can't fix it. Even when I stripped it down to the bare minimum it doesn't work. I uploaded the minimal project to: https://github.com/flocsy/garmin-onBackgroundData

The goal: after it logs "Background: Stats.onReceive: Background.exit:" we should see the log: "TestApp.onBackgroundData !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!"

Who can find the problem?

I did see the onBackgroundData being called once, when there was error -101, which is probably a bug in the simulator, but whenever I get real response or even if I change the hostname to some garbage and receive responseCode 404 it's not being passed back to the foreground app's onBackgroundData method

This is a shot in the dark, but I noticed you are calling Background.exit() from another file. 

I've found that things like this that should work and represent good modular design stretch the limits of what the Garmin team probably envisioned and tested to support.  I'll bet they only thought people would call Background.exit() from inside methods inside the class that extendsSystem.ServiceDelegate. Or if not that, some other weird limitation about where (file-wise) you call Background.exit().

Consider finding a way to get the Background.exit() call to be made from inside the StatsServiceDelegate class and see if that resolves it?

No it doesn't. Even if you look at my original example above you'll see that I added Baxkground.exit to MyServiceDelegate.onTemporalEvent() and it doesn't work even there. But it does work in MyServiceDelegate.initialize().

This has me scratching my head.  I wish I could help more.  Next time I get back in code, I'll explore if I can get the onBackgroundData to call reliably

import Toybox.System;

(:background)                    //------>   , :background_app)
class StatsServiceDelegate extends System.ServiceDelegate {

    function initialize() {
        // TODO: can it be removed?
        ServiceDelegate.initialize();
        log("StatsServiceDelegate.initialize");
    }
    
    function onTemporalEvent() as Void {
        log("StatsServiceDelegate.onTemporalEvent");
        Stats.onTemporalEvent();
    }
}

1:29:27 TestApp.initialize: true
1:29:27 TestApp.onStart: true
1:29:27 setStorage: Q = s
1:29:27 Stats.triggerTemporalEvent: 1:27:49, 1:32:49: s
1:29:27 TestApp.getInitialView
1:29:27 TestApp.onBackgroundData !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!: -101
1:29:27 Stats.onBackgroundData: -101
1:29:27 Stats.onBackgroundData: delete storage
1:29:27 setStorage: Q = null

flocsy🤠

-101 means you put too many webreqs

Web request result storage is limited (to 8k I read somewhere?) and it tripped me up. I had to result to implementing a loop by having the onReceive method call the web request again until the end of the list, then I could exit with a "done" status. I added a retry counter in case onReceive got errors so if retry count exceeded I could exit with an "error" status.

Not in this case. The respond has a few bytes.