json - Pagination while scrolling in Swift Firebase

Question

I am loading data from Firebase Database. I am trying to load data while user scrolls. For example if he has scrolled about 20 cells then I want to load a little more about 5 cells. I am trying to achieve it like this but it is not working:

func parseSnusBrands(){
        let ref = FIRDatabase.database().reference().child("Snuses").child("Brands")

        ref.queryOrderedByKey().queryLimitedToLast(20).observeEventType(.Value, withBlock: { (snapshot) in
            if snapshot.exists() {
                if let all = (snapshot.value?.allKeys)! as? [String]{
                    self.snusBrandsArray = all
                    self.snusBrandsTableView.reloadData()

                }
            }
        })
    }

and to detect how many cells are scrolled:

override func tableView(tableView: UITableView, willDisplayCell cell: UITableViewCell, forRowAtIndexPath indexPath: NSIndexPath) {
    if indexPath.row == 20 {
        let ref = FIRDatabase.database().reference().child("Snuses").child("Brands")

        ref.queryOrderedByKey().queryLimitedToLast(20).observeEventType(.Value, withBlock: { (snapshot) in
            if snapshot.exists() {
                if let all = (snapshot.value?.allKeys)! as? [String]{
                    self.snusBrandsArray = all
                    self.snusBrandsTableView.reloadData()

                }
            }
        })
    }
}

This is my Firebase structure:

Is there better solution or should I keep trying like this?

Here you can see the whole code. I know that it lacks of OO but I am learning :)

Answer 1

Waitting for answers