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

If a folder is placed in the Dock you can sort it by "date added" - this is usually 开发者_如何学Pythonthe 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

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;
}

Note: out of date now that Lion’s out.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

Here's a Swift 5.x version of Wojtek's answer:

public extension URL {
    var dateAdded: Date? {
        if let metadataItemValue = MDItemCreateWithURL(kCFAllocatorDefault, (self as CFURL)) {
            return MDItemCopyAttribute(metadataItemValue, kMDItemDateAdded) as? Date
        }
        return nil
    }
}

_{I've tested this back to Swift 4.x, and I think it'll compile without modification back to Swift 3.x if you need that too. Just be aware that, before Swift 5, its inferred visibility would be internal rather than public.}