How to show the share button in Mountain Lion?

To add the share button on Mountain Lion:

1) Add a NSButton called, for example, shareButton.

2) Add the standard image for this button:

[shareButton setImage:[NSImage imageNamed:NSImageNameShareTemplate]];
[shareButton sendActionOn:NSLeftMouseDownMask];

3) Into the "on click action", present the NSSharingServicePicker:

NSSharingServicePicker *sharingServicePicker = [[NSSharingServicePicker alloc] initWithItems:urls];
sharingServicePicker.delegate = self;

[sharingServicePicker showRelativeToRect:[sender bounds]
                                          ofView:sender
                                   preferredEdge:NSMinYEdge];

4) Eventually, implement the NSSharingServicePickerDelegate methods to customize the picker’s available services.