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 extremely easy in Snow Leopard:

- (void)deduplicateRunningInstances {
    if ([[NSRunningApplication runningApplicationsWithBundleIdentifier:[[NSBundle mainBundle] bundleIdentifier]] count] > 1) {
        [[NSAlert alertWithMessageText:[NSString stringWithFormat:@"Another copy of %@ is already running.", [[NSBundle mainBundle] objectForInfoDictionaryKey:(NSString *)kCFBundleNameKey]] 
                         defaultButton:nil alternateButton:nil otherButton:nil informativeTextWithFormat:@"This copy will now quit."] runModal];

        [NSApp terminate:nil];
    }
}

See http://blog.jseibert.com/post/1167439217/deduplicating-running-instances-or-how-to-detect-if for more information.