How to create Quick Look debug previews for your custom types

Swift version: 5.10

Paul Hudson @twostraws May 28th 2019

Xcode’s Quick Look debugging allows us to visually preview the value of our types, and is capable of showing numbers, strings, attributed strings, colors, images, PDFs, Bezier paths, and more.

By default your custom types don’t have a Quick Look preview, so you won’t see anything useful. But if you add the debugQuickLookObject() method to your type then you can return something you want from there to have it show up in Xcode:

class User {
    var name = "Duane Dibbley"
    var age = 28

    @objc func debugQuickLookObject() -> Any? {
        return "My name is \(name) and I'm \(age)."
    }
}

That will show a string inside Xcode, but you could also format the string with attributes, create an image of your game board, and so on.