Custom NSView Drag Destination

I'm trying to create a simple NSView that will allow a folder from Finder to be dragged onto it. A folder path is the only thing I want the view to accept as a draggable item. I've been trying to follow the Apple documentation, but so far nothing's working. So far, I've just tried to get the view to work with any file type, but I can't even seem to do that. Here's what I have so far:

-(id) initWithFrame:(NSRect)frameRect
{
    if (self = [super initWithFrame:frameRect])
    {
        NSLog(@"getting called");
        [self registerForDraggedTypes:[NSArray arrayWithObjects:NSPasteboardTypeString,
                                       NSPasteboardTypePDF,
                                       NSPasteboardTypeTIFF,
                                       NSPasteboardTypePNG,
                                       NSPasteboardTypeRTF,
                                       NSPasteboardTypeRTFD,
                                       NSPasteboardTypeHTML,
                                       NSPasteboardTypeTabularText,
                                       NSPasteboardTypeFont,
                                       NSPasteboardTypeRuler,
                                       NSPasteboardTypeColor,
                                       NSPasteboardTypeSound,
                                       NSPasteboardTypeMultipleTextSelection,
                                       NSPasteboardTypeFindPanelSearchOptions, nil]];
    }
    return self;
}

-(BOOL) prepareForDragOperation: (id<NSDraggingInfo>) sender
{
    NSLog(@"preparing for drag");

    return YES;
}

The initWithFrame: method is getting called, but when I try to drag into the view the prepareForDragOperation: method doesn't ever seem to get called. My questions:<