Receive custom URL schema in macOS

AppDelegate.swift

class AppDelegate: NSObject, NSApplicationDelegate {
    func applicationDidFinishLaunching(_ aNotification: Notification) {
        NSAppleEventManager.shared().setEventHandler(self, andSelector: #selector(self.handleGetURLEvent(event:replyEvent:)), forEventClass: AEEventClass(kInternetEventClass), andEventID: AEEventID(kAEGetURL))
    }

    @objc func handleGetURLEvent(event: NSAppleEventDescriptor, replyEvent: NSAppleEventDescriptor) {
        let urlString = event.paramDescriptor(forKeyword: AEKeyword(keyDirectObject))?.stringValue!
        let url = URL(string: urlString!)!
        debugPrint(url);
    }
}

Be sure to use urls with 2 slashes. So myscheme://something and not myscheme:something otherwise Safari will not recognize the scheme.

The Apple docs provide these examples for iOS which do not work in macOS:

myphotoapp:albumname?name=”albumname”
myphotoapp:albumname?index=1

https://developer.apple.com/documentation/uikit/inter-process_communication/allowing_apps_and_websites_to_link_to_your_content/defining_a_custom_url_scheme_for_your_app

You might need to close your browsers and then open your app before the scheme is recognized. Also, you might need to Product>Clean Build Folder in Xcode. At least when developing.