Office Hours Transcript: 2021-05-25

Hey Mark

Hey I’ve got an odd situation with Volley going on. Is that something you can brainstorm with me on?

Hmmm…ok. Do you use a different library for what it does?

ok - well the question also involves making sure I understand what is going on under the covers prior to me making a call to it.

I’m not sure it is a Volley thing, although I’ve walked through enough times in the debugger now where I think it is some sort of race condition in there.

What I use it for is to make HTTPS calls to an API that is the backend of my website.

Validating user credentials, etc. etc.

When the app starts up, the entire flow works flawlessly.

But, for example, on some Samsung phones I notice if the user pops out to the phone settings, then turns off a permission that my app has been previously granted by the user (access to the microphone for example), what Samsung does is actually restart the app.

When it does this, the Application class gets onCreate called, then whatever activity was previously active gets its onCreate called and so forth.

Standard stuff I guess

OK so when I go through the same initialization sequence on that startup, Volley freezes.

I’ve traced it far enough where I know it is making the web call, I know it is getting data back from the web server.

Then nothing.

No error, no nothing.

Just goes into a black hole.

If I step through it in the debugger, this does not happen.

Hence me thinking it is a race condition of some sort.

Me either

Except it doesn’t go through my "SplashActivity", which then would launch a main activity vs. going directly to "main" (or whatever other activity had previously been active)

Correct Volley does not

It also doesn’t call the error listener

It just…stops

And the app hangs, as if it is a deadlock on the UI thread

which it isn’t

Yes I understand why it isn’t called on the restart

I was just mentioning that because it isn’t exactly the same code path

Yes - my way to cause this behavior is to have the main screen of my app up.

Then hit the "multiple windows" button on the device (this is Samsung Android 8)

Swipe over to Settings

Change the permission

Then pop back to the app

It actually starts working until it hits that request of Volley to access my website

Doesn’t matter which web API I call - it’s all the same behavior

Right - I thought you were asking how I get it to fail

ok one sec

I think at the moment that I change the permission, it restarts the app before I can do anything

What you are calling the "overview screen" is the view I get when I tap the icon on this device which shows me recently run apps?

(It’s an older Samsung S7)

ok one second - I need to rebuild this app (another annoying issue I’m having with AS 4.2.1 is that it thinks it can’t delete the build directory for some reason, all of a sudden)…

Have you run into that with anyone else?

I assume it must be some sort of environment problem on my system, but I’ll be darned if I can tell.

Started happening when I upgraded from 4.1.3

Yeah I’m having to do full rebuilds now a bunch.

OK just so I am clear

I start the app, get it to the main screen where it normally gets ok.

Then I use the overview screen to go to settings, and change the permission?

Then I go back to the overview screen, and swipe left on my app?

Swipe off the screen - ok. I guess I don’t normally do that

ok going to settings

Swiped it off

It did not

Started normally

onDestroy() gets called in these cases?

Hmmmm. ok

I do have some "shut down" code where I stop the Volley Queue, clear out any pending requests, etc.

ok

Right

The weird thing is that I’ve verified that in both cases, the https call gets made and valid data comes back.

It is what is happening with that return value after that point that is different

Right.

For all other activities, I have a base class that extends AppCompatActivity, and in that class in onCreate and onResume I’m verifying that the Volley queue is initialized prior to anything else getting done.

For all other activities other than splashactivity I mean

So I can see that on re-entry to the app, those methods are getting called, and Volley is getting initialized.

And of course, like I said it actually makes the call and receives data.

So it isn’t the queue or queue mechanincs

Something else

Back to what you are doing - I haven’t used okHttp directly. Does it offer the high level functionality of Volley or would I have to roll my own?

here is an example:

public static void performNonBlockingHttpGet(String url,
                                             HashMap<String, Object> params,
                                             final Response.Listener<String> listener,
                                             final Response.ErrorListener errorListener,
                                             int timeoutInSeconds) throws Exception {
    String newUrl;
    Timber.d("Lifecycle: performNonBlockingHttpGet with timeout: %d url: %s, Volley queue shows %s entries.", timeoutInSeconds, url,getRequestQueueCount());
    Response.Listener<String> internalListener = response -> {
        decrementRequestQueueCount();
        try {
            listener.onResponse(response);
            Timber.d("Lifecycle: performNonBlockingHttpGet for %s ends normally.", url);
        } catch (Exception e) {
            Timber.e("Lifecycle: performNnBlockingHttpGet for %s ends in exception: %s", url, e.getMessage());
            throw e;
        }
    };
    Response.ErrorListener internalErrorListener = error -> {
        decrementRequestQueueCount();
        try {
            errorListener.onErrorResponse(error);
            Timber.d("Lifecycle: performNonBlockingHttpGet for %s ends with an error:%s.",url, error.getMessage());
        } catch (Exception e) {
            Timber.e("Lifecycle: performNonBlockingHttpGet for %s ends in exception: %s", url, e.getMessage());
            throw e;
        }
    };
    if (params != null) {
        newUrl = createGetRequestUrl(url, params);
    } else {
        newUrl = createGetRequestUrl(url, null);
    }

    StringRequest request =
            new StringRequest(Request.Method.GET,
                    newUrl,
                    internalListener,
                    internalErrorListener) {
                @Override
                public Priority getPriority() {
                    return Priority.NORMAL;
                }
            };
    request.setRetryPolicy(new DefaultRetryPolicy(timeoutInSeconds * 1000,
            1,
            DefaultRetryPolicy.DEFAULT_BACKOFF_MULT));
    addToRequestQueue(request, true);

I set two listeners, and make the Url call

Processing the result in my listeners

And its supported :)

How do I get around the fact that other libraries I am using (PubNub being one) also has their own dependency on OkHttp which may not be the version I would be using?

i.e. it is within their shipping library

Yeah, I was using okHttp originally for some other reason, and when I upgraded my PubNub stopped working correctly and those guys said "don’t do that"

So I dropped it

Which version?

of each?

I’m using PubNub 5.0.0

That’s a pretty recent version of OkHttp right?

Interesting

I think the OkHttp that they use internally is fairly old

Have you been pretty happy with PubNub? I’ve noticed a fair number of intermittent disconnects.

It generally will always reconnect, but I’ve had to really tighten down my recovery code.

Probably a good thing anyway

Is your client using it world-wide or just in one region?

Are you using the heartbeat mechanism?

I started, then stopped using it. For me decided it was ok to recover on re-connect rather than proactively detect disconnect.

Plus it costs extra $

I’ll look into OkHttp again, thanks.

Anything big on the horizon that you think is going to be a game-changer?

Android-wise?

Yep, that’s a good call.

Are they still supporting Flutter in a big way?

So continuing to gain steam in your opinion…

That’s the real question

o me

to me

I’ve read a few articles in the last 6 months or so of the "So I decided to give Flutter a try and compare it to Xamarin" (or <name your other favorite>)

https://leancode.pl/blog/lessons-learned-after-making-the-first-10-commercial-apps-in-flutter

OK - thanks again for your insights, gonna jet.