A swift PropertyWrapper to provide automatic NSView/UIView invalidation when the properties value changes. It duplicates the @Invalidating propertyWrapper for build targets prior to macOS 12 and iOS 15.

I saw in the WWDC2021 video 'What's new in AppKit' they make a brief mention of a new propertyWrapper type @Invalidating() that automatically updates views when the wrappedValue is changed. It appears this propertyWrapper is only available in later versions of AppKit (and presumably UIKit).

Given that a lot of AppKit/UIKit devs aren't going to be able to move their minimum target version to macOS 12 or iOS 15 soon I decided to try to replicate what I saw in the video.

@VIViewInvalidating() was born!

And once your target is set to macOS 13 or above, your @VIViewInvalidating() definitions will generate deprecation warnings telling you to move to @Invalidating().

I've tried to make sure that the APIs are as close to @Invalidating as possible so moving your app target should in theory be as simple as changing some names

• @VIViewInvalidating -> @Invalidating
• VIViewCustomInvalidating -> UIViewInvalidating (for iOS/tvOS)
• VIViewCustomInvalidating -> NSViewInvalidating (for macOS)

Provides built-in invalidators for

• needsDisplay (.display)
• needsLayout (.layout)
• needsUpdateConstraints (.constraints)
• invalidateIntrinsicContentSize() (.intrinsicContentSize)
• invalidateRestorableState() (.restorableState) [macOS only]

class BadgeView: NSView {
   // Automatically sets needsDisplay = true on the view when the value changes
   @VIViewInvalidating(.display) var color: NSColor = NSColor.blue
   
   // Set needsDisplay, needsLayout and invalidateIntrinsicContentSize() on 
   // the view when the value changes
   @VIViewInvalidating(.display, .layout, .intrinsicContentSize)
   var position: NSControl.ImagePosition = .imageLeft
}

The protocol method provides a very high-level callback when any of the @VIViewInvalidating properties are updated within your view. This is equivalent to the NSViewInvalidating protocol in later SDKs (macOS 12 and iOS 15)

class BadgeView: NSView  {
   @VIViewInvalidating(.display) var color: NSColor = NSColor.blue
   @VIViewInvalidating(.display) var backgroundColor: NSColor = NSColor.white
}

extension BadgeView: VIViewCustomInvalidating {
   // Will be called when any `@VIViewInvalidating` property is updated in the view
   func invalidate(view: NSView) {
      Swift.print("custom invalidation!")
   }
}

NOTE that this behaviour is NOT compatible with Apple's @Invalidating property wrapper. @Invalidating doesn't provide a similar functionality, so be aware when you move your build target up to macOS13/iOS15 there is no direct replacement so your code will break.

You can provide custom invalidators by defining a new class of type VIViewType.VIViewInvalidatorAction.

class CustomInvalidator: VIViewInvalidatorAction {
   public override func invalidate(_ view: VIViewType) {
      Swift.print("Custom invalidator called")
   }
}

class ExcitingView: NSView {
   @VIViewInvalidating(.display) var color: NSColor = .white
   @VIViewInvalidating(.display, CustomInvalidator()) var backgroundColor: NSColor = .systemBlue
   override func draw(_ dirtyRect: NSRect) {
      self.backgroundColor.setFill()
      dirtyRect.fill()
   }
}

• Fixed macOS demo linkage

• Added separate dynamic and static targets (thanks BeehiveInnovations)!

• Resolved Swift runtime crash when building in Xcode 11 and Swift 5.1. Previous version would crash the Swift runtime as it tries to resolve generic arguments for a class nested in an extension. Removing the nested extension containing the property wrapper (it wasn't required) solved the issue. This has no impact when compiling with Xcode 12 and above.

• [BREAKING] Now that Apple has made @Invalidating available through Xcode, I've changed custom callback to match Apple's 'Invalidating' protocol to aid adoption when upgrading the SDK to one that supports @Invalidating.
• [BREAKING] Changed the mechanism for handling custom invalidations.
• Added restorableState as an invalidation type on macOS to be compatible with @Invalidating on macOS 12+

• Initial release

Twitter, Swift By Sundell

• Accessing a swift property wrappers enclosing instance
• The power of subscripts in swift

MIT. Use it for anything you want! Let me know if you do use it somewhere, I'd love to hear about it.

MIT License

Copyright (c) 2021 Darren Ford

Permission is hereby granted, free of charge, to any person obtaining a copy
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