While working on a very large iOS client project, I was investigating the causes for our slow app launch time. We had a hypothesis that part of the problem was that too many view controllers were getting loaded in memory, in particular, ones that were not even being presented to the user during app startup. What could cause view controllers to load too early? How might you discover this happening? And how do you fix it? Let’s find out.

Continue…

If you have ever worked on an iOS app, you have definitely used UINavigationController. It has been around since iOS 2 and is a fundamental component in UIKit. Yet, there is one very powerful API that you might not know about.

Continue…

I’ve decided to deprecate one of my open source libraries, PresenterKit. The library has been in a sort of “maintenance mode” for awhile now. It never really became what I hoped and anticipated. I think it implemented some neat ideas and helped removed some boilerplate from UIKit, but I don’t think what it provided necessarily justified a library anymore — at least not given the lack of activity around the project.

Continue…

I previously wrote about implementing Dark Mode in an older codebase, specifically how Dark Mode works (or doesn’t) with CGColor. I recently fixed a bug in the same project that was difficult to track down because it manifested in such a strange way. After finding the problematic code, I realized that it is an extremely common scenario in iOS codebases — so you might have this bug in your code as well!

Continue…

I was recently working on a project that uses modern collection views on iOS — that is, using diffable data sources, snapshots, and cell providers. I hooked up all the components and my collection view was working, or so I thought. I started to notice some very odd, unpredictable behavior when the collection view was updated. Some of the time, the cells were updated correctly. Other times, I would see duplicates and missing data. Here’s what went wrong.

Continue…

This year at WWDC, some significant improvements and changes were announced for UICollectionView and UITableView. You can watch 10252: Make blazing fast lists and collection views for all the details, but I want to highlight some of them here.

Continue…

I’ve been following what’s going on with SwiftUI since it was released with iOS 13 at WWDC 2019 and have even taken extensive notes, but I have avoided using it. As I wrote before, I mainly wanted to avoid dealing with bugs and workarounds that might make me less productive compared to using UIKit, which I know quite well. I’m very interested in learning and using it, I’m just hesitant given some of Apple’s history, like early years of Swift. I have no doubt that SwiftUI will be the future of Apple platform development, the question is when that future will arrive. This year the framework is debuting its third major release in iOS 15. How far has SwiftUI come, and is it ready for building serious apps?

Continue…

Xcode’s UI testing framework has had its ups and downs over the years. Most recently, it has been much more robust and reliable in my experience. However, tests still tend to flake sometimes. Here are some ways that I have been able to reduce flakiness in UI tests.

Continue…

In JavaScript, this pattern is called an Immediately Invoked Function Expression (IIFE) or a Self-Executing Anonymous Function. Swift doesn’t have an “official” name for this, but IIFE works as well as “immediately executed anonymous closure” or “self-executing anonymous closure”. (Thanks to folks on Twitter for helping with this.)

Continue…

Swift’s strict initialization rules are great. They help prevent an entire category of bugs that were especially common in Objective-C. However, when working with Objective-C frameworks, particularly UIKit, these rules can be frustrating.

Continue…

Today I am deprecating my open source library, JSQDataSourcesKit. I have already marked the CocoaPod as deprecated and archived the repo on GitHub. I will not be taking additional contributions.

Continue…

For an iOS project that I am currently working on, I am implementing Dark Mode. The codebase is approaching 7 years old, it is mostly Swift with some legacy Objective-C, and it currently supports iOS 11 and above. Aside from the tedium of ensuring the updated colors are being used throughout the codebase, I expected this task to be straight-forward. However, there were some unanticipated issues.

Continue…

I recently needed to determine when the user has manually switched between dark mode and light mode on macOS. In my menu bar app, Lucifer, the icon reflects the current appearance setting when you change it from the app — an inverted pentagram for dark mode and an upright pentagram for light mode. But there’s a bug. If the user manually changes the appearance setting from System Preferences, or if they are using the new “auto” setting in macOS Catalina, the icon gets stuck in its previous state.

Continue…

This isn’t complicated, but I found it confusing. Perhaps I am spoiled by the more modern APIs in UIKit. When writing Lucifer, a menu bar app, I wanted to have different actions for left-clicking and right-clicking on the button in the menu bar. To my surprise, this was much more cumbersome than I expected.

Continue…

A few weeks ago, I spoke at Realm in San Francisco at the Swift Language User Group (#SLUG) meetup. A video of the talk is now online over at Realm’s blog, where it is synced with my slides. If you haven’t already seen it, go check it out!

Continue…

In iOS development, the core of nearly every app rests on the foundations provided by UICollectionView and UITableView. These APIs make it simple to build interfaces that display the data in our app, and allow us to easily interact with those data. Because they are so frequently used, it makes sense to optimize and refine how we use them — to reduce the boilerplate involved in setting them up, to make them testable, and more. With Swift, we have new ways with which we can approach these APIs and reimagine how we use them to build apps.

Continue…

Surprisingly, I have not seen anyone talking about what I just discovered in the iOS 9.0 API Diffs. (Well, actually what Max von Webel discovered.) There’s a hidden gem in the UIKit diffs. We no longer have to suffer through tracking down obscure bugs due to non-zeroing weak references.

Continue…