Loading WebP Images from UIPasteboard

February 24, 2021

I recently got a bug report for Transparent App Icons to the effect of "I tried to paste in a transparent image, but it didn't work." After cropping the background to create a "transparent" image users can use for their Shortcuts icons, the app allows the user to paste an image from the clipboard to overlay and create a semi-transparent icon - this user was trying to paste a WebP image...

Writing An App In 2 Days

December 17, 2020

This September, I developed and released an iOS app called Transparent App Icons. I wrote the app (or at least, the app’s initial version) very quickly, and it’s paid off in terms of the time I put into it - in addition to being a great learning experience from a technical and business perspective, it’s generated $3,000 in proceeds since launch, which means it’s the first app I’ve put on the App Store which will contribute nontrivially to my paycheck...

New SF Symbols in iOS 14

November 22, 2020

SF Symbols, the standardized icon system for the Apple ecosystem, got some great upgrades this year. In addition to macOS support, there are almost a thousand more symbols available, and there are some changes in the symbol names...

Creating a shared unit test utils library with Xcode

August 9, 2020

I've been talking a fair amount recently about how I've been writing a lot of unit tests for Fluency, my Confluence editor app, and how much I value having good tests to catch regressions and verify that the editor is actually working correctly. In the case of Fluency, I now have 70+ tests which test various parts of the app, and I've extracted various utils out of the actual...

Self-Sizing UITableView Cells with SwiftUI

July 21, 2020

It's been a year since SwiftUI was released, and many iOS developers who are lucky to only support the two most current iOS versions will soon be able to start writing SwiftUI in their production apps. There are clear benefits to using SwiftUI (I could probably devote a whole post to them), so the question I've been thinking about is: where to start?

Automatic preview updating paused

July 5, 2020

I've been rewriting parts of CIFilter.io in SwiftUI, and one issue I ran into recently was that SwiftUI previews didn't seem to work as advertised. When I opened the preview, it would trigger an app build, eventually show up, but there would always be a banner telling me that previewing had been paused...

SwiftUI Crash in AG::LayoutDescriptor::compare

July 3, 2020

I've been working lately on rewriting some of CIFilter.io in SwiftUI. One crash I came across that initially stumped me would happen when resetting my UIHostingController's rootView to a view that was equivalent to the one already set...

Expression shuffles the elements of this tuple; this behavior is deprecated

June 25, 2020

Whenever a new major version of Xcode is released, one of the first things I do is download it and run it with the various codebases I'm working on. Usually the new version of Swift is smarter and can surface more warnings and diagnostics, and the Xcode 12 beta release earlier this week (with Swift 5.3) is no exception...

SwiftUI: Two equal width columns

June 17, 2020

A problem that many people run into after writing enough SwiftUI is how to make it so that two views inside an HStack have equal width, such that if the HStack grows both inner views expand proportionally...

Swift Tip: Refactoring a Private Method for Testability

May 28, 2020

Writing testable Swift code is an ongoing process, so much so that you could write a book about it, but yesterday I was reminded of a really great insight I read long ago in Working Effectively with Legacy Code about testing private methods...

Nested Property Wrappers in Swift

May 11, 2020

You can nest property wrapers in Swift, but it's difficult. NSHipster has a great article about all things property wrappers, and the summary of trying to compose them (which others have echoed) is that it's hard and prone to compiler errors...

Writing a UserDefaults editor with SwiftUI and property wrappers

May 5, 2020

I've been talking a lot online about how useful SwiftUI has been in building debug components for Fluency - debug menus are one of the places where you can start using SwiftUI right now..

Animating Metal Content with CoreAnimation

December 10, 2019

Recently, I've been learning more about Metal - I'm still working through the basics, but I've written a couple of posts and tweets about it, and I'm about halfway through Metal By Example. Up until now I've mostly been coding sample projects, but I recently had the opportunity to prototype a Metal implementation integrated into our production app at work...

GPU Capture Button Flickering

October 28, 2019

One of the "Things I Don't Know" in the iOS ecosystem is Metal. As such, I've been working through Metal By Example recently, which still stands as a great introduction to Metal...

Relative date time formatting in SwiftUI

October 19, 2019

In the wild world of 2019 SwiftUI development, lots of things aren't documented. One such thing I ran into recently was the usage of RelativeDateTimeFormatter in a Text view...

ColorCompatibility Library

October 5, 2019

I wrote previously about a technique I use in Trestle and CIFilter.io to support iOS 12 and lower while still using system provided, dark-mode accessible colors...

iOS 13 UIWindowScene Black Screen

September 21, 2019

I've encountered this bug enough times that I figured it was time to write a quick post about it. If you've looked into multiple window support for your app in iOS 13, you might know that a lot of the setup you used to have to do in the app delegate now lives in the scene delegate instead...

Popovers, UINavigationController, and preferredContentSize

August 26, 2019

In this post we'll look at a very specific but tricky interaction in UIKit, one which took me multiple days to work out how to implement. It's two view controllers of different sizes, pushed on a UINavigationController, which is presented as a popover. The view controllers...

The application's CFBundleVersion is invalid

August 22, 2019

For some reason lately, I've been having a lot of trouble installing apps and running tests in the iOS simulator on Xcode 10 (non-beta). The error message looks like this...

Taking Down Assets from SFSymbols.com

August 20, 2019

At the beginning of June, I launched sfsymbols.com since there wasn't a reference available on the web for searching and filtering the list of 1500+ system icons included in...

Backwards compatibility for iOS 13 system colors

June 9, 2019

At WWDC 2019, Apple announced that Dark Mode would be supported on iOS 13. There are some significant changes to UIKit in order to support this - many of them are detailed in the talk Implementing Dark Mode on iOS which I'd highly recommend watching...

UIButton: Padding Between Image and Text

May 6, 2019

Pop quiz: in a UIButton, how do you set a padding of 10pt between the image and the title? I had to do this at work recently, and I was surprised at how hard it was to reason about. There are several posts talking about this topic (including this one which uses edge insets to flip the title and image!), but the answer for my use case was pretty hard to find...

Passing data through the App Store with UIPasteboard

April 15, 2019

About a year ago I wrote a puzzle game called Trestle. If you download it using any of the links in this post (by clicking on them on your iOS device), you'll get a nice Easter egg and two of the (normally paid) level sets enabled for free...

CIFilter.io (Core Image Filter Reference)

March 31, 2019

Today I'm launching CIFilter.io 🎉 CIFilter.io is a project I've been working on for the last few months, and today it's open source. It has two parts...

CIVector Codable

March 5, 2019

For my current side project, I have to export CIFilter parameters to json, and I've been running into issues with various CoreImage types not conforming to Swift's Codable...

Dead Simple Dependency Injection in Swift

February 15, 2019

At the most recent Swift Language User Group meetup, Patrick Barry presented a great talk about how Lyft implements dependency injection. I'd highly recommend watching the video - I was impressed by how clean and...

iOS Color Wheel Using CIFilter

January 28, 2019

After struggling for some time with CIFilter documentation at work, I've been working on an app which can apply filters interactively for various inputs...

RxSwift: Multiple subscribers for a unit of work

December 8, 2018

I've been working on a side project for better CIFilter documentation lately, and I decided this was as good of a time as any to try out RxSwift. We use reactive programming at work, but I haven't really been able to dig into it yet...

Installing Nokogiri from a Gemfile on Mojave

November 14, 2018

Another MacOS and another struggle through installing nokogiri. Most places online recommend using...

How NOT to set nil in UserDefaults

October 22, 2018

To clear a value from UserDefaults, I previously thought it was fine to do something like this:

UserDefaults.standard.set(nil, forKey: "myKey")

Turns out that this works differently in different iOS versions. Starting in iOS 11, setting nil for a key works as I expected.

Casting a pointer to UInt in Swift

October 16, 2018

There are some times in Swift, like when using System Trace, that you want to get the pointer value of an object directly as a UInt (passing the pointer to kdebug_signpost is one). I was surprised at how hard it was to find documentation on how to get a Swift reference’s pointer value as a UInt.

NSObject Equality is Tricky

November 13, 2016

Swift can be tricky sometimes. For example, what does the following print?

class A: NSObject {
  let x: Int

  init(x: Int) {
    self.x = x
func ==(left: A, right: A) -> Bool {
  return left.x == right.x
print(A(x: 1) == A(x: 1))
print([A(x: 1)] == [A(x: 1)])