Touch ID and Face ID on iOS

Introduction Adding support for Touch ID and Face ID to your app is not always completely straightforward, especially given that the documentation from Apple on the APIs is somewhat sparse and in some cases incorrect. I recently added Face ID and Touch ID support to my company’s app and I thought it would be helpful to document what I found. There is only a single class, LAContext in the LocalAuthentication framework, so it’s surprising how complex it can get. »

Swift and KVO context variables

I came across a crash in my app Memories when using the iOS 11 betas. It happened reliably every time I loaded a video, and the video code uses KVO, as AVFoundation requires you to use it for a lot of things. When I ran the app in Xcode this was the exception that was causing the crash: Simultaneous accesses to 0x1c41ded68, but modification requires exclusive access. Previous access (a modification) started at addObserver(_:forKeyPath:options:context:) Current access (a modification) started at observeValue(forKeyPath:of:change:context:) The hex address was the address of the property I was using as the context passed to addObserver() and which I was checking in observeValue. »

Using PHLivePhotoView with Auto Layout

So, I was working on updating my app Memories to support displaying Live Photos properly and not just as a static image. I took a look at the documentation for PHLivePhotoView and thought that this would be fairly straightforward. For Live Photos, I’ll just use a PHLivePhotoView instead of a UIImageView. Well, as is usually the case when a developer says: “this looks straightforward, I’ll have it done in a couple of hours”, it was not quite so straightforward and had me scratching my head and cursing until 2am until I finally realised what I was doing wrong. »

Comparing Dates, whilst ignoring the time

Comparing dates is one of the most common things you have to do as a developer of almost any type of software. At first glance it would seem to be something almost trivially easy. What could possibly go wrong? Well, turns out, quite a lot! I’m going to highlight just one issue that recently caused an embarassing bug in my app Memories. It involved just a simple date comparison, ignoring time, and without crossing timezones. »

Using stride to convert C-style for loops to Swift 2.2

With the release of Swift 2.2 in Xcode 7.3 C-style for loops have become deprecated. The default Xcode fix-it for converting them uses a Range: let count = 5 for var index = 0; index < count; index++ { doSomething(index) } is converted do: let count = 5 for index in 0 ..< count { doSomething(index) } For the vast majority of C-style for loops this will work perfectly well. »