Fun with SwiftUI – Beta 3

After being abruptly stopped last time by a compilation step that would not complete in a finite amount of time, I let the project rest until Beta 3 was released.

I could probably have found my mistake, but I was also willing to give it another two weeks and then see whether the compiler would just tell me what I was doing wrong.

Which, when Beta 3 was released, it actually did. Trying to recompile the project would immediately be stopped at a clear error message (I don’t actually remember the details any more), but the fix was very easy after all.

Motivated to finally move on, I finished hooking up my state handler to the UI itself and I was finally at a point where I would run this skeleton in the simulator.

Simulator says: nope.

First the good news: Apple was right when they proudly said that they have improved the watch simulator workflow: Launching the simulator in stand-alone mode finally is a sub-second endeavor and so is actually launching your app in the debugger.

Working this way is actual honest-to-god fun.

Yes, things should just work like this out of the box, but until now, they never did: Running the watch simulator meant also running the phone simulator and proxying all debugger operations through the phone simulator, including breaking connections and horrible, horrible lag.

But none of this still happens in WatchOS 6: The simulator can run on its own and it launches instantly. No connection issues.

At least not to talk to Xcode…

My initial excitement about things working so well was abruptly dampened by the fact that all network access I was trying to do in the simulator ended up failing with a generic error and in the log output some backend component would complain about losing connection to the background transfer service.

Of course I first assumed to be the source of the problem and I spent two hours trying to find out what I was doing wrong.

I shouldn’t have, because my last resort was to check the Apple Beta forums and there, I didn’t even have to bother posting a question: Others had the issue too and the solution is to just use a real device.

Onwards to the real device

Updating a watch to a Beta OS is a tricky proposition: There is no (official) way to ever downgrade and stuff is known to be shaky.

Also, my watch is the one single computer I use that produces data for which I have no backup and re-creating the data is a (literally) painful experience.

I’m talking about workout data.

For two years now I’m running 10ish km every day and while I know rationally that the actual act of running is what counts, unfortunately, my subconscious only accepts a run as having happened when it’s also tracked in the Activity app and when the rings are closed.

So would I dare updating to a beta version knowing that I can’t downgrade and that the watch is producing irreplaceable data that I heavily rely on?

Of course I would. 🤓

But only after checking our local electronics retailer to make sure that they had a replacement watch on stock if worse comes to worst. Yes. I know that you can ask Apple to downgrade a bricked/unsuable watch, but that would mean days without the watch and days without my runs being tracked.

Inacceptable.

Anyways. Updating to watchOS 6 went fine and a small test walk around my house has shown that tracking workouts was still generally working fine. So I was all set to try it on the real device.

Moving forward on the device

The good news: While not as fast as the simulator, deploying and debugging on the watch still is considerably quicker and more reliable than it ever was on any previous combination of Xcode, iOS and watchOS.

Debugging still involves proxying though the phone, but now it’s reliable. Over the course of 4 weeks of doing this (spoiler alert), I only had one or two instances where Xcode wouldn’t talk to the watch and more and I had to restart my computer, my phone and my watch to get connectivity restored.

Judging by other people’s prior experiences, this is a huge step forward.

The other good news: Network requests to indeed work on the real device. My client could fetch a JWT token from the smide.ch service and it could get a list of currently available bikes.

Impressive rendering speed

I have chosen the most naïve implementation possible and just fed the whole list of ~200 bikes directly into the UI framework. No dealing with cell reuse, no limiting the size of the list, nothing. Just “hey SwiftUI, please render this list of 200 bikes”.

And render it does: It’s quick and scrolling through the whole list is buttery smooth without doing any kind of optimization work. And once the next roadblock is fixed (see below) and the list gets dynamically re-sorted as my location changes, that too is buttery smooth.

I’m getting away with telling the framework that the list has changed and needs repainting and I just pass it a new updated list of bikes. The change is instantaneous. Even though it’s a new list of 200 items.

This is so much fun. I shouldn’t need to care about minimizing updates. I shouldn’t need to care about cell reuse. I shouldn’t need to deal with this. And with SwiftUI, I don’t have to.

Location roadblocks

Excited, I moved forward to asking for location access and using location to sort the list of bikes.

And this is where things ground to a halt.

Whenever my independent watch app extension would be launched, I would be calling CLLocationManager.authorizationStatus() which would tell me that my status was .notDetermined, so I would ask for permission.

My delegate callback would be called with .authorizedWhenInUse, but CLLocationManager.authorizationStatus() would still return .notDetermined and all attempts at calling location specific API would be ignored.

As this was my first strides into CoreLocation, I assumed this to be my fault and spent a lot of time debugging this, moving code around and trying out things, but not matter what I did, the effects didn’t change.

Then I tried Apple’s Sample Code from 2016 which of course worked fine even after I changed the integrated watch app to be usable independently.

After a few more hours of trial and error, I finally was able to pin it down though: In Beta 3 (and presumably earlier Betas too), the CoreLocation permission management is broken if your watch app is a completely independent watch app.

If it has a companion iOS app, then requesting location permission is fine, but when you have a watch app without any iOS app which has a plist that looks like this:

<key>WKWatchOnly</key>
<true/>

Then requesting location permission would trigger a race condition where your permission is simultaneously granted and not granted.

I could have caved and made an empty iOS companion app at this point, but I decided to report this issue using Feedback Assistant and call it another two weeks.

The relief I felt when I’ve seen Apple’s official code sample to fail the same way as my sample code did the moment I set that WKWatchOnly flag was one hell of a feeling.

I wasn’t doing it wrong. I wasn’t losing my mind.

Next time, things will finally fall into place, but only after dealing with deprecations.

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