This is a stellar walkthrough of, well, as it says,
For example, what if you want to build a control to help the user select an Angle value between 0 and 360?
A solution would be to create a circular slider and let the user drag the knob to select the angle value. This is something you’ve probably already seen in many other interfaces but nothing similar is available in UIKit.
That’s why this is the perfect example we can use to set aside UIKit and build something special. But first, here’s a sneak peek of what we are going to create…
Some nifty little CoreGraphics and trigonometry tips to boot; worth reading even if you’re already familiar with control writing.
Another topic that goes nicely with writing a control is making it support UIAppearance skinning — so along with that, check out
In the simplest case, add UI_APPEARANCE_SELECTOR to your properties to inform others that this property can be set via an UIAppearance proxy. There are however some gotchas that are not clearly mentioned in the documentation, and it’s always interesting how something like this works behind the scenes…
Good tips there it’d take you a fair bit of confusion to sort out on your own!
h/t: iOS Dev Weekly!