How to list out Recently Opened documents in iOS?

Question

I have listed out all the documents in NSDocument Directory and im able to get the documents that are recently modified using :

NSMutableArray* filesAndProperties = [NSMutableArray arrayWithCapacity:[filesArray count]];
for(NSString* file in filesArray) {
    NSString* filePath = [iMgr.documentsPath stringByAppendingPathComponent:file];
    NSDictionary* properties = [[NSFileManager defaultManager]
                                attributesOfItemAtPath:filePath
                                error:&error];
    NSDate* modDate = [properties objectForKey:NSFileModificationDate];

    if(error == nil)
    {
        [filesAndProperties addObject:[NSDictionary dictionaryWithObjectsAndKeys:
                                       file, @"path",
                                       modDate, @"lastModDate",
                                       nil]];                 
    }
}

by fallowing : Get directory contents in date modified order

Now how can i list out the documents that have been opened and viewed by the user without any editing or modifications ?