How to show last tableView cell WITHOUT scrolling effect

Question

I am trying to create a comments / messages tableView using Swift and would like for the UITableViewController to show the last tableViewCell when the user clicks that "comment room"

I am pulling data from a remote source, (Firebase in this case) to populate each of the tableViewCells. Once I pull all the data, I configure each cell with the appropriate information. This is done without any error whatsoever.

However, by default, the tableview shows the cell at the top

I've tried using these to make the tableView show the last cell but it still performs a visible "scrolling" effect which I would like to remove. For example, take the iMessage app, Instagram's or Snapchat's direct messaging feature. Upon clicking a "chat or comment room", the resulting table (or collectionview) immediately displays the last cell without visibly scrolling to it

Here is what I tried:

var chatRoomMessages: [FIRDataSnapshot] = []

override func viewDidLoad() {
    super.viewDidLoad()

    fetchChatRoomCommentsFromServer(chatRoomId: self.chatRoomId) { (snap) in
        self.chatRoomMessages.append(snap)
        self.tableView.reloadData()

    }
}

override func viewDidAppear(_ animated: Bool) {
    super.viewDidAppear(animated)
    moveToLastComment()
}

func fetchChatRoomCommentsFromServer(chatRoomId: String, callback: @escaping (FIRDataSnapshot) -> ()) {
    DataService.dataService.CHAT_ROOM_REF.child(chatRoomId).child("messages").observe(.childAdded, with: { (snapshot) in
        DataService.dataService.MESSAGES_REF.child(snapshot.key).observe(.value, with: { (snap) in
            callback(snap)
        })
    })
}

func moveToLastComment() {
    if self.tableView.contentSize.height > self.tableView.frame.height {
        // First figure out how many sections there are
        let lastSectionIndex = self.tableView!.numberOfSections - 1

        // Then grab the number of rows in the last section
        let lastRowIndex = self.tableView!.numberOfRows(inSection: lastSectionIndex) - 1

        // Now just construct the index path
        let pathToLastRow = NSIndexPath(row: lastRowIndex, section: lastSectionIndex)

        // Make the last row visible
        self.tableView?.scrollToRow(at: pathToLastRow as IndexPath, at: UITableViewScrollPosition.bottom, animated: true)
    }
}

The messages are laoded properly and the view does scroll to the last tableViewCell as intended....BUT...I want the view to already appear at that last cell. Along with the three app examples, I've seen other apps do the same thing.

Any help would be greatly appreciated

EDIT: 3:26pm November 17

I've also tried putting the moveToLastComment() function call in viewDidLoad after the reloadData(), viewWillAppear and viewDidAppear. No change. In fact, when I put it anywhere other than viewDidAppear, absolutely nothing happens. I have to scroll down as usual

Answer 1

To respond to @shallowThought: Again, implementing viewWillAppear does absolutely nothing to the view. No movement of any kind. The TableViewController loads all the data but remains at the very top. However, I did try implementing viewDidAppear again and viewWillAppear together. I believe viewWillAppear couldn't work alone because you can't reload a tableView when the tableView itself has not "appeared" or "loaded". viewWillAppear seems to work more with fetching data, configuring separator styles, etc. So this is what I did:

override func viewWillAppear(_ animated: Bool) {
    super.viewWillAppear(animated)

    self.navigationController?.setToolbarHidden(true, animated: true)
    self.tableView.separatorStyle = .none
    self.tableView.setNeedsLayout()
    self.tableView.layoutIfNeeded()
    self.tableView.rowHeight = UITableViewAutomaticDimension
    self.tableView.estimatedRowHeight = 80

    NotificationCenter.default.addObserver(self, selector: #selector(SingleChatRoomTableViewController.keyboardWillShow(notification:)), name: NSNotification.Name.UIKeyboardWillShow, object: nil)

    NotificationCenter.default.addObserver(self, selector: #selector(SingleChatRoomTableViewController.keyboardWillHide(notification:)), name: NSNotification.Name.UIKeyboardWillHide, object: nil)

    DispatchQueue.global().async {
        DataService.dataService.fetchChatRoomCommentsFromServer(chatRoomId: self.chatRoomId) { (snap) in
            self.chatRoomMessages.append(snap)
        }
    }
}


override func viewDidAppear(_ animated: Bool) {
    super.viewDidAppear(animated)
    DispatchQueue.main.async {
        self.tableView.reloadData()
        self.moveToLastComment()
    }
}

This works the way I intended; The tableview loads at the very last cell without visibly scrolling to that row or visibly "teleporting" to that row. Whether or not it visibly scrolls or teleports is the difference between specifying true or false in the scrollToRow method call. This way does neither, the view is simply waiting at the very last row without showing the user.

HOWEVER... the actual cells that display the messages are somewhat slow to load. Perhaps this is due to the nature of Firebase or how I'm loading the data. The tableView itself seems to "know" where the last message-row will be, but the actual content messages have to load which is still visible. In any case, that's a topic for another question.

Answer 2

Set animated to false:

self.tableView?.scrollToRow(at: pathToLastRow as IndexPath, at: UITableViewScrollPosition.bottom, animated: false)

Also, delete viewDidLoad and viewDidAppear and implement viewWillAppear instead:

override func viewWillAppear(_ animated: Bool) {
    super.viewWillAppear(animated)

    fetchChatRoomCommentsFromServer(chatRoomId: self.chatRoomId) { (snap) in
        self.chatRoomMessages.append(snap)
        self.tableView.reloadData()
        moveToLastComment()
    }
}

Answer 3

I needed similar behavior but went down a different path than you which doesn't require any of the scrolling code. In mine, the most recent messages ("comments") are always inserted at the top of the list. To make them appear at the bottom of the screen, I set the transform of the UITableView:

self.tableView.transform    = CGAffineTransformMakeScale(1, -1);

This makes an "upside down" tableview, which is no good since all the cell content is also upside down. You can fix that with:

- (void) tableView: (UITableView *) tableView willDisplayCell: (UITableViewCell *) cell forRowAtIndexPath:(NSIndexPath *) indexPath
{
    cell.transform = self.tableView.transform;
} 

As long as the user hasn't manually scrolled away, any new incoming messages are inserted nicely, pushing the other messages "up".