class GZFeedTableViewController: UIViewController {
    lazy var postsRef = Database.database().reference().child("posts") // this is a path to the posts array in my Firebase database
    var posts = [GZPost]()                      // holds all the posts once they are downloaded
    var loadingPostCount = 0                    // equal to the number of posts already downloaded, plus the number currently downloading.
    var idOfFinalPostInNextQuery: String?       // used so that when we query database, we know where to go from
    let noOfPostsToLoad = 5                     // the number of posts loaded in each query
    @IBOutlet weak var tableView: UITableView!  // my tableview from the storyboard
    override func viewDidLoad() {
        super.viewDidLoad()
        self.tableViewSetup()                   // set up the tableview - see below
        self.loadSomeMorePosts(self.noOfPostsToLoad)    // this method does the querying and loading of posts
    }
    private func tableViewSetup() {
        self.tableView.register(UINib.init(nibName: "GZFeedTableViewCell", bundle: nil), forCellReuseIdentifier: "GZFeedTableViewCell")
        let refreshControl = UIRefreshControl() // allows you to pull down on the UITableView to reload.
        let title = NSLocalizedString("Pull to refresh", comment: "Pull to refresh")
        refreshControl.attributedTitle = NSAttributedString(string: title)
        refreshControl.addTarget(self, action: #selector(refreshOptions(sender:)), for: .valueChanged)
        tableView.refreshControl = refreshControl
    }
    @objc private func refreshOptions(sender: UIRefreshControl) {
        self.reloadFeed()
        sender.endRefreshing()
    }