var fetchingMore = false

func scrollViewDidScroll(_ scrollView: UIScrollView) {
    let offsetY = scrollView.contentOffset.y
    let contentHeight = scrollView.contentSize.height

    if offsetY > contentHeight - scrollView.frame.height * 4 {
        if !fetchingMore {
            beginBatchFetch()
        }
    }
}

func beginBatchFetch() {
    fetchingMore = true
    
    //Load more data from server
    DispatchQueue.main.asyncAfter(deadline: .now() + 0.25, execute: {
        //Mark that job is done
        self.fetchingMore = false
        self.tableView.reloadData()
    })
}