UIActivity represents an icon that appears in UIActivityViewController's view (the share menu in iOS 6).
Ordering
You can force a custom activity to appear before another activity by returning the other activity's type string in the method:
-[UIActivity _beforeActivity];
You must also return YES in
-[UIActivity _canAdjustOrder];
Custom image
If you return an image from the method -[UIActivity activityImage] then the alpha will be used as a mask for the metallic grill background. In order to have a custom full-colour icon, return the image from this method:
-[UIActivity _activityImage]