Find the Last Accessed Date of a File in Cocoa
The C way of doing it, using the stat system call will work in Objective-C.
e.g.
struct stat output;
int ret = stat(aFilePath, &output);
// error handling omitted for this example
struct timespec accessTime = output.st_atime;
You should get aFilePath by sending -fileSystemRepresentation to an NSString containing the path.
Another way you might get what you want is to construct an NSURL fore a file URL pointing to the file you want and using -resourceValuesForKeys:error: to get the NSURLContentAccessDate resource value.
Using NSMetadataQuery you can access spotlight metadata from your code. The last used date attribute of a file is tracked by spotlight and you can access that with this property: kMDItemLastUsedDate.