Behind the App: Wallaroo

It’s been awhile since I’ve done one of these deep dives on what goes on behind the scenes during the development of an Iconfactory app. There’s a common thread to each one: I feel the need to document our work when there’s a major change in how we build user interfaces.

The first one was for the “flattening” of Twitterrific 5, a task that preceded Apple’s work in iOS 7 by six months. The next one was for Flare 2, when the Aqua face of macOS began a dramatic evolution in Yosemite.

With Wallaroo, there’s another major change that may not be noticeable on the surface: it’s the Iconfactory’s first app written completely in SwiftUI.

A Discovery

It all started while I was working on Shortcuts support in Tot. During March of this year, I noticed that there was an action to “Set Wallpaper”. I also learned how Shortcuts could be downloaded, installed, and managed using a URLs.

The Iconfactory has been making wallpaper images since the dawn of time, but it never made sense to make an app because changing your wallpaper was a manual task. Shortcuts radically changed this calculus and the idea for an app was born. I threw together a quick prototype that let you set two wallpapers. Sean and I had the beginnings of Wallaroo.

Our wallpaper prototype became one of those “we’ll do it some day” projects. Then something important happened: WWDC 2022. After Lock and Home Screen customization was announced, the idea immediately became a “we need to do this before September!” project.

Time is Tight

We built Wallaroo from scratch in a little over two months.

The project started with a couple of wrinkles: the “Set Wallpaper” action didn’t work with the new features on iOS 16, so we filed FB10377111 on June 6th (a couple of hours after the keynote ended). We placed our faith in the abilities of the Shortcuts team and decided to carry on in spite of this setback. (We wish everyone at Apple wrote release notes like they do!)

The other wrinkle was that we all had work-in-progress that needed to be finished up. We knew that the short timeframe meant that this was an “all hands on deck” situation, so it wasn’t until the end of June before we all freed up. We put the prototype on TestFlight and got to work.

Divide and Conquer

There were three major areas where we focused our attention:

  • Content – Hundreds of wallpapers had been created over the years, but resolution and aspect ratio varied widely. Things needed to be cleaned up.
  • Backend – Over years, we had done releases in an ad-hoc manner: uploading ZIP files to a Patreon account would no longer be acceptable. We needed a server to manage the wallpapers.
  • Frontend – An app to display the wallpapers: it had to look and work great. Sexy and fast were primary design goals.

Ged, Anthony, Dave, and Talos immediately got to work on the first bullet, but without a backend server, there was no place to put files and metadata. So we made a Numbers spreadsheet and shared it in Dropbox along with the source images. Our Slack channel for the project was filled with “I’m going in” and “I’m out!” to avoid write conflicts. (S.W.A.T. = Software Write Avoidance Technique)

I was responsible for the development of the backend. Importing a spreadsheet CSV file gave us our initial database and images in Dropbox let me manually generate thumbnails and other content that would be needed in the app.

Sean took the lead on the app. We’ve been holding back on SwiftUI due to its immaturity, but the changes in iOS 16 looked great, so we went all in (the only UIKit/AppKit code is in delegate connectors). The data in the spreadsheet was massaged again to give him some real data to use.

Talos took the lead on the app architecture and the wireframe was finished on July 5th. A week later we had enough working code to make a Git repository. A few days later Sean showed us his Captain Pike Appreciation App:

We were on our way, but had less than two months before an iPhone announcement. Time to kick butt.

Butt Kicking

July was a blur. Progress was quick and everyone was heads down on their app responsibilities.

Remember that bug in Shortcuts that prevented Set Wallpaper from working in iOS 16? It was still around and we were starting to get worried. When iOS 16 beta 5 dropped on August 8th, we rejoiced when our test ran. The shortcut action worked perfectly!

Our last update to the shared spreadsheet was on August 10th. From that point on, we were able to use our new content management system to add and update wallpaper. There was still a ton of work needed to clean up metadata and fine tune each wallpaper release.

With the new server up and running, we started testing push notifications. Since Sean’s focus was still in the primary user interface, I started working on the SwiftUI views and models that talked to our backend server. That work continued with integrating the Patreon API and hooking up StoreKit2 for subscriptions. I also had a blast doing the User License and Credits screens.

We started our first beta test with Patreon supporters on August 25th. We were going to make the mid-September release date!


Looking back on the development, I think there were two things working in our favor: experience and SwiftUI.

We’ve made a lot of apps and have an instinctual knowledge on how to build them. But no matter how little friction there is in working together, you still have to put the pieces together.

SwiftUI is incredibly good at doing that.

Keep in mind that neither Sean or I had created a full-fledged app using SwiftUI (widgets don’t count). We had to learn the idioms and best practices, but once that was overcome, development happened at a lightning pace.

We encountered roadblocks, of course. Tracking down memory leaks was harder than UIKit because of the abstractions. Figuring out how to share an image was a huge head scratcher. Implementing parallax in a ScrollView was many days of hard work. And you should see the comments in our PagingView!

But overall, the experience was extremely positive. If you’ve been on the fence with this technology, iOS 16 feels like a turning point in SwiftUI’s evolution.

Give It a Go!

Now that you’ve read about how we made it, take Wallaroo for a spin. It’s a FREE download and a fun little app for iOS 16. And a great example of what you can do with SwiftUI.