How to detect whether an OS X application is already launched

Question

Normally an application bundle on OS X can only be started once, however by simply copying the bundle the same application can be launched twice. What\'s the best strategy t

Answer 1

This is a combination of Romans' and Jeff's answers for Swift 2.0: If another instance of the app with the same bundle ID is already running, show an alert, activate the other instance and quit the duplicate instance.

func applicationDidFinishLaunching(aNotification: NSNotification) {
    /* Check if another instance of this app is running. */
    let bundleID = NSBundle.mainBundle().bundleIdentifier!
    if NSRunningApplication.runningApplicationsWithBundleIdentifier(bundleID).count > 1 {
        /* Show alert. */
        let alert = NSAlert()
        alert.addButtonWithTitle("OK")
        let appName = NSBundle.mainBundle().objectForInfoDictionaryKey(kCFBundleNameKey as String) as! String
        alert.messageText = "Another copy of \(appName) is already running."
        alert.informativeText = "This copy will now quit."
        alert.alertStyle = NSAlertStyle.CriticalAlertStyle
        alert.runModal()

        /* Activate the other instance and terminate this instance. */
        let apps = NSRunningApplication.runningApplicationsWithBundleIdentifier(bundleID)
        for app in apps {
            if app != NSRunningApplication.currentApplication() {
                app.activateWithOptions([.ActivateAllWindows, .ActivateIgnoringOtherApps])
                break
            }
        }
        NSApp.terminate(nil)
    }

    /* ... */
}