In the What’s New in Cocoa for macOS session at WWDC 2018, Apple announced Quick Actions, which are handy little contextual tasks you can invoke on selected items in the Finder, either from a contextual menu or from the Preview side panel.
The emphasis in the session was on creating Quick Actions via Automator. There, it’s as simple as creating a new workflow document, selecting “Quick Action” from the template palette, and saving. It even puts it in the right place (~/Library/Services).
Essentially, Quick Actions appear to be macOS Services, which have a long history and which Automator has previously been able to create. In fact in macOS Mojave betas, the Quick Action document seems to completely supersede the “Service” type.
But what about native applications that want to provide Quick Actions? I didn’t see anything in the WWDC session to address this scenario, so I started poking around myself. When you click the “More…” button in Finder’s Preview panel, it opens up System Preferences’s Extensions settings, focused on a special “Finder” section. In the list are several built-in extensions.
I thought these were likely to be implemented as binary app extensions, so I instinctively control-clicked on one. A “Reveal in Finder” option appeared, so I selected it. Sure enough, they live inside Finder itself, and are packaged as “.appex” bundles, the same format that Apple supports for 3rd-party applications.
What’s handy about finding an example of an app extension you want to emulate, is you can open up its bundle and examine the Info.plist. Apple’s approach to identifying app extensions’s capabilities and appearance is based heavily on the specification of values in an NSExtension entry. Looking at one of Apples models, I saw confirmation that at least this variant was of type “com.apple.services” and that its attributes included many useful values. NSExtensionActivationRule, are substantially documented, and can be used to finely tune which types of target items an extension can perform useful actions on.
Others, such as NSExtensionServiceAllowsFinderPreviewItem and NSExtensionServiceFinderPreviewIconName do not appear to be publicly documented yet, but one can guess at what their meaning is. I’m not sure yet if the icon name has to be something public or if you can bundle a custom icon and reference it from the extension. I was alerted on Twitter to at least one other key: NSExtensionServiceAllowsTouchBarItem, which evidently triggers the action’s appearance in the Touch Bar while a qualified item is selected.
Dumping AppKit’s framework binary and grepping for likely matches reveals the following key values which are pretty easy to guess the meaning of:
NSExtensionServiceAllowsFinderPreviewItem NSExtensionServiceFinderPreviewLabel NSExtensionServiceFinderPreviewIconName NSExtensionServiceAllowsTouchBarItem NSExtensionServiceTouchBarLabel NSExtensionServiceTouchBarIconName NSExtensionServiceTouchBarBezelColorName NSExtensionServiceToolbarPaletteLabel NSExtensionServiceToolbarIconName NSExtensionServiceToolbarIconFile NSExtensionServiceAllowsToolbarItem
Of course, until these are documented, and even when they are, until macOS Mojave 10.14 ships, you should consider these all to be preliminary values which could disappear depending on further development by Apple of the upcoming OS.