Swift 2 iOS - get file list sorted by creation date - more concise solution?

Question

In my code, which works, I am returning a [String]? containing the names of the files (lastPathComponent) stored in /Documents/ - ordered by the date last modified.

I believe that I am probably using too many steps and am looking for advice here re how to reduce the code.

In order to achieve the required result currently - I am creating two intermediate dictionaries: var attributesDictionary: [String : AnyObject]? and var urlDictionary = [NSURL:NSDate](). Looping through the initial [NSURL] I am using two steps - .resourceValuesForKeys initializes attributesDictionary. I then populate urlDictionary so that it contains the URL and the value for the key NSURLContentModificationDateKey.

I feel fairly certain that there should be a way to achieve this result without creating urlDictionary and attributesDictionary and without the need for the loop. Perhaps from urlArray directly. Here is my current code:

EDIT: do{}s were not required as pointed out by Arthur Gevorkyan in the first comment.

func getFileList() -> [String]? {
    let directory = NSFileManager.defaultManager().URLsForDirectory(.DocumentDirectory, inDomains: .UserDomainMask)[0]
    let properties = [NSURLLocalizedNameKey, NSURLCreationDateKey, NSURLContentModificationDateKey, NSURLLocalizedTypeDescriptionKey]

    // no catch required - contentsOfDirectoryAtURL returns nil if there is an error
    if let urlArray = try? NSFileManager.defaultManager().contentsOfDirectoryAtURL(directory, includingPropertiesForKeys: properties, options:NSDirectoryEnumerationOptions.SkipsHiddenFiles) {
        var attributesDictionary: [String:AnyObject]?
        var dateLastModified: NSDate
        var urlDictionary = [NSURL:NSDate]()

        for URLs in urlArray {
            // no catch required - resourceValuesForKeys returns nil if there is an error
            attributesDictionary = try? URLs.resourceValuesForKeys(properties)
            dateLastModified = attributesDictionary?[NSURLContentModificationDateKey] as! NSDate
            urlDictionary[URLs] = dateLastModified
        }
        // this approach to sort is used because NSDate cannot be directly compared with </>
        return urlDictionary.filter{$0 != nil}.sort{$0.1.compare($1.1) == NSComparisonResult.OrderedDescending }.map{$0.0}.map{$0.lastPathComponent!}
    } else {
        return nil
    }
}

Answer 1

A possible solution:

if let urlArray = try? NSFileManager.defaultManager().contentsOfDirectoryAtURL(directory,
    includingPropertiesForKeys: properties, options:.SkipsHiddenFiles) {

    return urlArray.map { url -> (String, NSTimeInterval) in
        var lastModified : AnyObject?
        _ = try? url.getResourceValue(&lastModified, forKey: NSURLContentModificationDateKey)
        return (url.lastPathComponent!, lastModified?.timeIntervalSinceReferenceDate ?? 0)
    }
    .sort({ $0.1 > $1.1 }) // sort descending modification dates
    .map { $0.0 } // extract file names

} else {
    return nil
}

The array of URLs is mapped to an array of (lastPathComponent, lastModificationDate) tuples first, then sorted according to the last modification date, and finally the path name extracted.

The attributesDictionary can be avoided by using getResourceValue(_ : forKey) to retrieve only the last modification date.

Update for Swift 3:

let directory = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask).first!
if let urlArray = try? FileManager.default.contentsOfDirectory(at: directory,
                                                               includingPropertiesForKeys: [.contentModificationDateKey],
                                                               options:.skipsHiddenFiles) {

    return urlArray.map { url in
            (url.lastPathComponent, (try? url.resourceValues(forKeys: [.contentModificationDateKey]))?.contentModificationDate ?? Date.distantPast)
        }
        .sorted(by: { $0.1 > $1.1 }) // sort descending modification dates
        .map { $0.0 } // extract file names

} else {
    return nil
}