How can a Mac app determine the method used to launch it?

Question

I have a Mac OS X application that is also a protocol handler (just as, for example, Safari is a protocol handler for the HTTP and HTTPS protocols). So when a user clicks a link of the form myscheme://some-kind-of-info in any application at all, my application launches to handle the link.

Now I need to be able to determine if the application was launched by such a link click, or if it was launched by any other method. In other words, it was launched by any method besides a link click. (In those cases, I want the app to stay open, but if it was launched by a link it should quit and ignore the link. This way it only operates when already running.)

Is there some way within the app at startup to introspect and find out that it was launched by a standard method rather than by an AppleScript GetURL event? I'd like to find out through a documented method, rather than - for example - just have my app only open these links after it's been running for a half a second.

Answer 1

You can register a handler for each of the possible Apple Events you'll get on launch, and make note of which one you receive first.

• If the application is launched without documents, you'll get kAEOpenApplication.
• If it's launched with documents, you'll get kAEOpenDocuments (or kAEPrintDocuments).
• If it's launched with a URL, then (obviously) you'll get kAEGetURL.

There's also kAEOpenContents, but I wasn't able to trigger it easily in my test app; it's probably worth supporting no matter what.

How Cocoa Applications Handle Apple Events documents all of this stuff.

There is one error in there, though; it says that AppleScript's "launch" will send kAEOpenApplication. It won't, it'll send ascr/noop (kASAppleScriptSuite/kASLaunchEvent, defined in ASRegistry.h). I couldn't get the usual Cocoa event handler mechanism to trap this event, so you may need to do some more digging there.

One way you can check if the event is sent at launch is to register the event handlers in your application delegate's applicationWillFinishLaunching: method; they should deliver by the time applicationDidFinishLaunching: is invoked. With that method, you could potentially only check for kAEGetURL.