这个怎么样？

- (unsigned long long) sizeOfFolderAtPath:(NSString *)path {
    NSArray *files = [[NSFileManager defaultManager] subpathsOfDirectoryAtPath:path error:nil];
    NSEnumerator *enumerator = [files objectEnumerator];
    NSString *fileName;
    unsigned long long size = 0;
    while (fileName = [enumerator nextObject]) {
        size += [[[NSFileManager defaultManager] fileAttributesAtPath:[folderPath stringByAppendingPathComponent:fileName] traverseLink:YES] fileSize];
    }
    return size;
}