I thought it would be a good idea to round up the various pieces of sample code I've created for Mac Catalyst just to get everything in one place. These are by no means step-by-step guides, merely illustrated examples that have come about over the course of developing my own apps and responding to questions from developers.
No license or attribution is required for any of these codebases. Most, if not all of them, require macOS 11. While Catalyst is present and supported in macOS 10.15, it lacks the Mac idiom (Optimized for Mac) which renders some of this optimization for macOS moot.
Preference Windows
CatalystPrefsWindow showcases how to add a SwiftUI-based preferences panel to your Catalyst app, using a custom window scene.
Translucent sidebars in SwiftUI
CatalystSwiftUISidebar demonstrates a way to wrap UISplitViewController in SwiftUI to get a translucent sidebar in your app.
Advanced three-column app shell & search toolbar item
advancedcatalystexample — I took the core of my new app, Scarlet, and rewrote it as an example app. It shows one method of building a three-column app, and includes some AppKit glue to add a search field in the toolbar.
Building a menu bar app (NSStatusItem) that uses HomeKit
airqualitymonitor shows a method of adding a menu bar item — an NSStatusItem — from a Catalyst app, in this particular case using HomeKit, a framework only available to Catalyst. It also hides the main app window, and its Dock icon, so that it's only visible from the menu bar.
Basic sidebar/toolbar app
CatalystSidebarToolbar is a trivial example just showing how to get a macOS 11-style sidebar & toolbar using UIKit.
Mini document app with color & font pickers
SmallText — although not intended as sample code, it happens to be a mini-app built with Catalyst that could be instructive. It uses the UIKit document model to open files, and demonstrates using a respresented file as a titlebar for your window.
AppleScript/Cocoa Scripting in Catalyst (also with SwiftUI)
CatalystAppleScript will show you everything you need to add AppleScript support to your Catalyst app. Perform commands (with arguments), set variables, read variables.
macOS Services in Catalyst
CatalystServices shows you how to set up a Services provider in your Catalyst app, and relay the results from AppKit back to your main codebase.
Catalyst Controls Gallery
Catalyst Controls Gallery is a demonstration of many common controls available to Mac Catalyst as of macOS 11.
Flare
Flare is a simplistic web browser for macOS built using UIKit. It demonstrates a custom address field toolbar item using an NSTextField subclass, bridged via AppKit, tabbed windowing, dynamic menu updates & window state restoration.