This package provides property wrappers that can be used on properties for any value conforming to ClosedRange to allow for super fast iteration of UIs and interactions without the need to wait to recompile / relaunch an application. It does so by automatically adding an interactive slider for any property that you annotate with @Adjustable that sits on top of your app's window so you can dynamically adjust properties and see them update live. It's powered by a lot of the stuff I experimented with to make SetNeedsDisplay.

This is perfect for adjusting animation parameters on-the-fly, tweaking constants, or refining things until they feel just right without needing to constantly recompile your app and allowing you to focus on making things feel great.

It uses a lot of neat runtime tricks to pull out the name of the variable so it can appropriately name the relevant slider and also features a collapsible menu that you can tuck away when you don't need it (powered by Motion!).

• Usage
• Installation
  • Requirements
  • Swift Package Manager
• License
• Thanks
• Contact Info

Annotate your property of a type that conforms to ClosedRange like so:

class MyView: UIView {

    // A slider from `0.0` to `100.0` starting at `20.0` will be created.
    // Anytime the slider is changed, `invalidateForAdjustable()` is called on the enclosing class.
    @Adjustable(0.0...100.0) var someCustomProperty: Double = 20.0

    // A slider from `0.0` to `100.0` starting at `20.0` will be created.
    // Anytime the slider is changed, the `valueChanged` block is called with an instance of `self` that you can reference as well as the new value.
    @Adjustable(0.0...100.0, valueChanged: { enclosingSelf, newValue in
      // access `self` via `enclosingSelf`
      // do what you want with `newValue
    }) var someOtherCustomProperty: Double = 20.0

    override func invalidateForAdjustable() {
      print("someCustomProperty: \(someCustomProperty)")
      print("someOtherCustomProperty: \(someOtherCustomProperty)")
    }

}

You can also use @Published!

class MyCoolClass {
  
  @Adjustable(0.0...100.0) var somePublishedProperty: Double = 20.0

  var publishedCancellable: AnyCancellable?

  init() {
    self.publishedCancellable = $someProperty.sink { newValue in 
      print("somePublishedProperty: \(somePublishedProperty)")
    }
  }
  
}

It also works in SwiftUI!

class Model: ObservableObject {

  @Adjustable(0.0...255.0) var somePublishedProperty: Double = 20.0

}

struct MyView: View {
  
  @StateObject var model = Model()

  var body: some View {
    Rectangle()
      .foregroundColor(Color(hue: model.colourOffset / 255.0, saturation: 1.0, brightness: 1.0))
  }
  
}

Anytime any slider is adjusted, invalidateForAdjustable will be called on the enclosing class. This by default calls setNeedsLayout on UIView and UIViewController's view, but this can be overridden and used to update the view's state or perform any action, really. There's also an inline block that can be supplied that contains an instance of the enclosing class (enclosingSelf) as well as the new value from the slider. ObservableObject invalidation is also supported and it will automatically call the correct objectWillChange event.

If you wish to override the default invalidation behaviour of UIView or UIViewController you can adopt the AdjustableInvalidation protocol:

import Motion

class MyView: UIView {

  @Adjustable(0.0...1.0) private var springResponse: Double = 0.5

  var springAnimation = SpringAnimation<CGFloat>(response: 0.5, damping: 1.0)

  func invalidateForAdjustable() {
      springAnimation.configure(response: springResponse, damping: 1.0)
  }

}

I've saved a lot of time using Adjustable in conjunction with Motion for rapid iteration of animation constants (e.g. springs). I'll try an animation, tweak it, try it again, and tweak it some more etc. Once finished, I'll update the constant inline and remove the @Adjustable. This saves so much time and allows you to focus on adjusting interactions to feel as best they can be (instead of waiting for Xcode to build and run again).

Another thing I use it for is layout constants that are referenced in layoutSubviews. Adjusting the slider will change the value, invalidate layout automatically (via setNeedsLayout), and call layoutSubviews which makes iteration really easy.

• iOS 17+
• Swift 5.9 or higher

Currently Adjustable supports Swift Package Manager.

Add the following to your Package.swift (or add it via Xcode's GUI):

.package(url: "https://github.com/b3ll/Adjustable", from: "0.0.1")

Adjustable is licensed under the BSD 2-clause license.

Thanks to @harlanhaskins and @hollyborla for helping point me in the right direction and explain the complexity that this sort of solution entails.

More info here.

Feel free to follow me on Mastodon: @b3ll!