[ios] Getting list of files in documents folder

What is wrong with my code for getting the filenames in the document folder?

func listFilesFromDocumentsFolder() -> [NSString]?{
    var theError = NSErrorPointer()
    let dirs = NSSearchPathForDirectoriesInDomains(NSSearchPathDirectory.DocumentDirectory, NSSearchPathDomainMask.AllDomainsMask, true) as? [String]
    if dirs != nil {
        let dir = dirs![0] as NSString
        let fileList = NSFileManager.defaultManager().contentsOfDirectoryAtPath(dir, error: theError) as [NSString]
        return fileList
    }else{
        return nil
    }
}

I thought I read the documents correctly and I am very sure about what is in the documents folder, but "fileList" does not show anything? "dir" shows the path to the folder.

Swift 5

// Get the document directory url
let documentsUrl =  FileManager.default.urls(for: .documentDirectory, in: .userDomainMask).first!

do {
    // Get the directory contents urls (including subfolders urls)
    let directoryContents = try FileManager.default.contentsOfDirectory(at: documentsUrl, includingPropertiesForKeys: nil)
    print(directoryContents)

    // if you want to filter the directory contents you can do like this:
    let mp3Files = directoryContents.filter{ $0.pathExtension == "mp3" }
    print("mp3 urls:",mp3Files)
    let mp3FileNames = mp3Files.map{ $0.deletingPathExtension().lastPathComponent }
    print("mp3 list:", mp3FileNames)

} catch {
    print(error)
}