Marley's Blog
Background
Over the past year I worked as part of a group developing a mobile application using React Native. The big advantage of React Native is that you can simply write the app once and have it work on both iOS and Android. To improve my understanding of app development, I thought I'd try making an app in SwiftUI, which is Apple's language for making iOS apps.
The first step was to update XCode, as I hadn't used it since before SwiftUI was released. This proved to be a fairly difficult step due to a combination of a large download size and a small SSD. After it was up to date, I watched some videos about the language and did the official Apple tutorials. Then I felt ready to take a step out on my own.
Calculator alligator
I decided on a calculator because it offers some challenges but is not too complex for a first project. In terms of the design of the app, I went for pretty much the stock iOS calculator look.
The colours are managed using an xcasset catalogue, so they can be modified without changing any code. It also copes brilliantly with dark mode and accessibility features.
Once the design was mostly done, it was time to implement the functionality. Whilst the adding, subtracting etc. were simple to implement, getting it working with the interface was a bit tricky. One of the saving graces was using EnvironmentObjects to store data that needed to be accessed throughout the app (such as the display value). I implemented this in a class called DataStoreXD, instantiated as appData.
Bugs!
I will now tell you about some of the bugs I encountered, as a cautionary tale. The first bug was that if a calculation resulted in a value greater than 999 it would crash the app, even though the user could manually type a number much large than that with no issue. This really stumped me, until I explained the issue to someone and it immediately clicked in my head that 1000 was the first value being displayed with commas in it. Even once I had figured this out, it took me a while to understand why this was crashing the app. It was because the commas were being added in two places, and the second was expecting to receive a number not a string. At least I could solve the problem using only the backspace key.
Another bug was that if the user typed a number, then pressed an operation button, then entered the same number, any additional input would override the value. This is as a result of a cheeky thing I was doing where I would compare the current screen value to the cached value to see if the value should be overrided (as it should be if the value is 0 or if an operation button has been pressed). The solution to this was to remove that silly logic and add a global flag to determine if input should override the value.
I also had quite a bit of trouble with getting the value to be constrained in length. This was essentially a problem with using < rather than ≤, AKA off by one error (OBOE).
In conclusion…
Other than that, though, things pretty much went without a hitch. I may do some more work on it, fixing any bugs that appear, improving the splash screen and the icon, and maybe making the style a bit more unique. However, I feel like I have already spent quite a large amount of time on this given that it isn't really that useful. In conclusion, I am a big fan of Swift and SwiftUI, and I hope I can use them on similar projects in the future. Maybe even something that's slightly interesting.
Thanks for reading! If you wish to continue this magical journey, head over to the Github repo.