Firebase Remote Config: Can't read any values, but fetch is successful

Workaround found! See below

I'm running into the "silent completion" thing - I call "fetch" but onComplete, onSuccess, or onFailure listeners never fire. I tried moving it to an activity onCreate, and still nothing happened, and therefore, the config items never get loaded from the server. I've got Developer Mode enabled, and am calling fetch with a cache value of 0.

I was able to (once) put a breakpoint on the line "public void onComplete(@NonNull Task task) {", which got hit, and then I was able to step through and the onComplete fired. I was then unable to reproduce this same result any other way, including doing the same thing (I think) a second time.

Seems like a timing or concurrency issue, but that makes little sense, given this is an asynchronous call.

Workaround

If you fetch from Activity#onResume (or, I presume, Activity#onStart), it works perfectly. Calling fetch from Activity#onCreate or Application#onCreate results in a call that seemingly never gets handled, and in fact, performance of the app degrades noticeably after the fetch begins, so I think there's a looper running or something.*

Workaround #2

If you really want this to run from Application#onCreate (which I do), this seems to work as well:

new Handler().postDelayed(new Runnable() {
    @Override
    public void run() {
        // Run mFirebaseRemoteConfig.fetch(timeout) here, and it works
    }
}, 0);

You're likely hitting the caching in Remote Config. The way it works is that Config will cache incoming items locally, and return them. So your last (cached) fetch status was probably before the value was defined, and we get a cached blank value.

You can control the cache expiry, but if you fetch too often you risk getting throttled.

Because this is a common development problem though, there is a developer mode that lets you request more rapidly (for small groups of users):

FirebaseRemoteConfigSettings configSettings = 
    new FirebaseRemoteConfigSettings.Builder()
        .setDeveloperModeEnabled(BuildConfig.DEBUG)
        .build();
FirebaseRemoteConfig.getInstance().setConfigSettings(configSettings);

When you call fetch you can then pass a short cache expiration time

long cacheExpiration = 3600;
FirebaseRemoteConfig mFirebaseRemoteConfig = FirebaseRemoteConfig.getInstance();
if (mFirebaseRemoteConfig.getInfo().getConfigSettings().isDeveloperModeEnabled()) {
     cacheExpiration = 0;
}
mFirebaseRemoteConfig.fetch(cacheExpiration)
     .addOnCompleteListener(new OnCompleteListener<Void>() {
     // ...
});

That's how its done in the quickstart sample if you want a full reference.

Found the problem.

After adding some logging, I found that the fetch job's onComplete() was never being called. I moved the fetch from my Application's onCreate to a fragment's, and now it works properly!

(Ian Barber, this might be something to look into or clarify, as the logs indicated that Firebase was initialized without an issue when it was in the Application, and the fetches were silent failures.)