Category: software

After a lot of momentum in Beta 4 where I finally got my rogue smide.ch client for the watch to work, Beta 5 and 6 were a bit of a letdown with regards to real-world usability.

Already with Beta 4, Apple has deprecated @ObjectBinding and BindableObject, both of which total staples of SwiftUI and totally required for you to do any kind of meaningful application because they provide the glue by which you hook your UI up to you actual application.

With this, even the last pieces of sample code shown at WWDC sessions about SwiftUI were now invalidated. What a breakneck speed of development.

On the other hand, this was also a case of parallel evolution inside Apple because all the old pair provided was also provided by the Combine framework with latter having the advantage of actually be usable not just in SwiftUI but anywhere in your applications.

So I can completely understand the reasoning behind the deprecation. If you are willing to clean this up, then the beta period is the time to do it.

However in Beta 4 on watchOS, while the old method was deprecated, the new way only worked partially: If you changed your class that was previously inheriting from BindableObject to now inherit from the correct Combine.ObservableObject, none of your publishes would actually be picked up by SwiftUI and the UI would remain static.

So in Beta 4, even though it was deprecated, I kept using BindableObject because that’s what was working. @ObjectBinding on the other hand, I could replace with @ObservedObject

But then, Beta 5 happened and the Beta 4 app crashed on startup.

Trying to compile it lead to a linker error because BindableObject now was gone for good. Note that the compiler was still just complaining about it being deprecated, but at link time, the symbol was missing and linking failed. This would also explain the crash at startup of the old Beta 4 app.

I’ve quickly replaced BindableObject with Combine.ObservableObject which made the app build again and run fine – on the simulator

On the real hardware, it would continue crashing on launch.

Even after installing the logging profile on the watch in order to get some information via the Console, all I got was a single log line entry from Carousel complaining about the launched process shutting down.

As this is just a fun project after all, this is where I stopped again, waiting what further betas will bring.

After a while, Beta 6 came and went. It brought no change.

Then, Beta 7 happened, but I didn’t even bother trying to recompile without an updated Xcode which finally happened today and, spoiler alert, my App is back in a running state. No further changes were required.

So it all wasn’t my fault after all.

Next time I’ll talk about the changes I’ve done since Beta 7 and Xcode Beta 6

After hitting yet another wall with Beta 3, the moment Beta 4 was released I’ve updated all my devices, recompiled the application and looked at it on the watch.

This time, without any change on my part, things just fell into place:

Location permission worked correctly. I had my list of Bikes sorted by location

What I didn’t like as much though were all the deprecation warnings I was already accumulating. During this years Beta Period, none of the APIs presented at WWDC were finalized. SwiftUI and Combine are still very much in flux and the APIs change on a biweekly basis.

At the time of this writing, Beta 5 has already removed all older deprecations and has added even more deprecations. We’re now at a point where most of the videos from WWDC sessions that are explaining SwiftUI and combine are not applicable to the real world any more, but that’s for another post.

Some lipstick on the pig

With things mostly working right, there was one thing that was bugging me in the list of bikes you’re seeing in the screenshot above: The distances to my current location were manually formatted in meters, but I knew that Apples platforms come with very good locale dependent unit formatters, so I wanted to fix that.

MeasurementFormatter has a .naturalScale unit option that’s supposed to pick scale and unit automatically dependent on the user’s locale. In case of distances, here in Switzerland, I would expect a distance to be shown in meters up until 1 km at which point I would expect a distance to be shown in km with one fractional digit of accuracy.

But that’s now what MeasurementFormatter does: It insisted on using km and it insisted on three fractional digits of accuracy. That’s why I’ve decided to format on my own. But I knew there must be a proper solution.

It tuns out, there is – but it’s part of MapKit, not of Foundation: There’s MKDistanceFormatter to use for this and while MeasurementFormatter has a unitOptions property, the MKDistanceFormatter has a unitStyle property which you can set to .abbreviated to get to the proper effect.

So I have added that and also used battery icons based on SFSymbols to display the bikes battery levels like so:

Reactive warts in SwiftUI

Remember when I said that the whole UI hierarchy was going to be built from one parent SwiftUI view that would decide on a state object? That’s the design I totally went with:

My main ContentView is just a big switch statement, completely exchanging its subview hierarchy dependent on what the global state handler object thinks should be currently active.

As you can see in above code, there’s only .ListingBikes – there’s no state to list a single bike. That’s fine, because that’s up to that BikeList view to decide to instead of listing a list of bikes it wants to show a single bike.

I did this using a NavigationLink nee NavigationButton setting its destination to the detail view:

What’s nice is that you get a free sliding animation and a free back button out of this. However, what’s not as nice is that if you do this, the detail view gets pushed as another native view on top of the existing view.

Which means that even when the big switch statement from the screenshot above causes a different sub-view to be rendered (and it does get rendered), then the additional view pushed by the NavigationLink remains shown on top and does not get closed.

In the end, here on Beta 4, I went with a NavigationDestinationLink so I could first close the detail view and then tell the state handler I wanted to create a booking.

At the time of this writing (Beta 5 has just been released), NavigationDestinationLink is already deprecated again and the state whether the destination is showing or not can be passed as a $binding, however, also at the time of this writing, this currently messes with the free back button

Another thing that falls in the same bucket of re-painting the whole hierarchy does not in fact repaint the whole hierarchy is a SwiftUI View’s navigationBarTitle modifier: if you set that once on any subview, it will persist even through you removing that subview and replacing it by another which doesn’t use the navigationBarTitle modifier.

Meaning that setting a property on a subview as an effect on global state.

This feels wrong to me.

First booking

Anyways – enough complaining. With all of this in place, I did my very first commute with a smide bike using nothing but my watch. Here you see me at the end of the trip, ready to end the booking:

That felt great.

What doesn’t feel great is the mess Beta 5 made out of my nicely layouted UI. But that’s for another day.

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.

After spending the first two weeks of the beta period to get a foundation going, I was eager to start working on the actual watch app.

This was right about the time when Beta 2 hit, so first I’ve upgraded to that and then started with the Watch project.

Building the UI

Eager to play around with SwiftUI, the first thing I have done was to actually just create a skeleton UI:

What immediately sprang to my mind as I was working on this was the fact that the built-in preview feature of SwiftUI forces you to keep your views self-contained and to keep the dependencies small and to keep your data easily mockable.

Otherwise you will suddenly be in the position where your Xcode preview requires working network connections and a lot of application state.

I’ve also learned that Beta 2 was still on very shaky grounds before running the actual code even once: My attempts to display a map view caused Xcode to crash completely the moment it tried to paint the UI preview, so I’ve stubbed that out to just be a rectangle

But overall, designing (if you can call it that) the skeleton UI went very quickly (a matter of a few hours) and I was eager to hook everything up.

A hard stop

After working on the UI, the next step was to produce a backend that orchestrates the actual application state. This single class is the only thing that keeps track of state in the application and based on which the UI decides what to paint and how and where the UI will call into in order to change the overall state (for example when the user logs in or when they start a booking)

This is what (at the time) you would use @ObjectBinding and BindableObject for.

My next step, thus, was to create what I called the ApplicationStateHandler which I had implement the BindableObject protocol.

That handler itself would expose a state property which could have one of various values of an ApplicationState enum. The main SwiftUI view would basically be a huge select statement over that state property and then decide what actual view to render based on the state.

This was my plan, but no matter what I did, the moment I had ApplicationStateHandler implement the BindableObject protocol, I would put Xcode 11 Beta 2 in a state where it was using 100% of each of my 8 CPU cores while trying to compile my code.

So in the end, I wasn’t stopped by incomprehensible error messages (I got my share of those too), but by a compilation run that did not seem to want to complete in finite time.

Instead of solving the halting problem, I decided to wait another two weeks because I already had other non-project related things on my plate.

Stay tuned for next time to see what stopped me hard in Beta 3

As explained before, I’ve decided to scratch my own itch and write an independent Apple Watch client for the smide.ch bike sharing service.

The first step to getting from the idea to the final watch app wasn’t actually involving the Watch at all: Before I could get started, I needed to know how the existing smide clients actually work and how to talk to their server.

Then I wanted to have a unit-tested library that I could use from the Watch Frontend.

On top of that library, I wanted to have a command-line client for easier debugging of the library itself.

And only then would I start working on the frontend on the watch.

Preliminaries

So as the Developer Beta 1 for XCode 11, WatchOS 6 and Catalina rolled out, the first few days of development I spent reverse-engineering the official Smide Client.

As always, the easiest solution was to just de-compile their Android Client and lo and behold, they are making use of retrofit to talk to their server which lead to a very nice and readable interface documentation right in my decompiler

Armed with this information, a bit of grepping through the rest of the decompiled code and my trusty curl client, I was able to document the subset of the API that I knew I was going to need for the minimal feature-set I wanted to implement.

In order to have a reference for the future, I have documented the API for myself in the OpenAPI format

This is useful documentation for myself and if I should ever decide to make the source code of this project available, then it’ll be useful for anybody else wanting to write a Smide client.

Moving to XCode: SmideKit

Now that I had the API documentation I needed, the next step was to start getting my SmideKit library going.

Even though there are tools out there that generate REST clients automatically based on an OpenAPI spec, all the tools I looked at produce code that relies on third-party libraries, often Alamofire. As XCode 11 was in a very rough shape already on its own, I wanted to minimize the dependencies on third-party libraries, so in the end, I’ve opted to write my own thin wrapper on top of URLSession

SmideKit is a cross-platform (by Apple’s definition) library in that the code itself works across all of Apple’s OSes, but there are individual targets for the individual OSes

But by manually setting the Bundle Name to $(PRODUCT_NAME) in the individual Info.plist files, I can make sure that all projects can just import SmideKit without any suffixes.

As this library is the most crucial part of the overall project, I have written unit testes for all methods to make sure we correctly deal with expiring tokens, unresponsive servers and so on.

The command line client

The first user of SmideKit would be a macOs command-line frontend called smidecli. It would offer various subcommands for listing bikes, booking them and ending bookings.

Here’s a screenshot of me booking a bike

Going from nowhere to the working command-line client has taken me the whole period of Beta 1. Two weeks is a long time but between my actual day job and my newly put upon me parenting duties, my time was a bit limited.

Still. It felt good to go from nowhere to writing a library, writing a command-line frontend and then actually using it to book a bike. On the other hand: None of the code written at this point had anything to do with the announcements of WWDC. All work done could just as well have been done on the old SDKs. But still: Having a good foundation to stand on, I was sure was going to pay off.

Next time: Adventures in Beta 2