Where does the Finder obtain the "date added" of an item in a folder?

Question

If a folder is placed in the Dock you can sort it by "date added" - this is usually the default for the Downloads folder. (Sometimes the Finder does not appear to be using the date added but the date modified, but it can find the date added.) Where is the Finder figuring this out from? The standard file metadata, i.e. as obtained by stat, getattrlist or FSGetCatInfo) does not contain it. TIA

Answer 1

Yep, the date added could be inferred from other structures. In fact, it resides in Spotlight metadata.

NSDate *dateAdded(NSURL *url)
{
    NSDate *rslt = nil;
    MDItemRef inspectedRef = nil;

    inspectedRef = MDItemCreateWithURL(kCFAllocatorDefault, (CFURLRef)url);
    if (inspectedRef){
        CFTypeRef cfRslt = MDItemCopyAttribute(inspectedRef, (CFStringRef)@"kMDItemDateAdded");
        if (cfRslt) {
            rslt = (NSDate *)cfRslt;
        }
    }
    return rslt;
}

Answer 2

Note: out of date now that Lion’s out.

The Finder isn’t, the Dock is. It tracks this data internally. If you remove a folder and put it back, the “date added” information is lost for existing items.