Prevent UITableView from scrolling when new cells are inserted - ios

Question

I've seen this question being asked several times and, despite having implemented each proposed solution by the community, I still haven't succeeded. What I'm implementing is a basic public chat app. I need to display many messages that I receive through my API inside a UITableView. In order to have a chat feeling, I've turned both my UITableView and UITableViewCell upside down by changing their transform property to CGAffineTransform(scaleX: 1, y: -1). Instead, to add cells to the UITableView, I first add the incoming message to the array via messages.insert(message, at: indexPath.row)and then I call insertRows(at: [indexPath], with: animation) (where indexPath is created this way IndexPath(row: 0, section: 0)). When I'm at the bottom of the UITableView everything works great: the new cells appear from bottom to top accompanied by a smooth animation. The problems start when I scroll to top by a few pixels. Take a look at these images to better understand the difference.
What I would like to achieve is preventing the UITableView from scrolling unless I'm at its very bottom so that, if the user scrolls to top with the aim of reading a past message, he can do so without any trouble caused by the movement of the UITableView.
I hope someone can point me in the right direction. Thanks
Edit: I'm using automatic UITableViewCell height if that helps.
Edit: here's my current code:
I'm using a generic wrapper class ListView<Cell: UITableViewCell, Item> with this method used for adding new items:
func add(_ item: Item) {
items.insert(item, at: 0)
if contentOffset.y > -contentInset.top {
insertRows(at: [IndexPath(row: 0, section: 0)], with: .top)
} else {
reloadData()
}
}
I had to use -contentInset.top to check if I'm at the very bottom of the scroll view since I've previously set the contentInset to UIEdgeInsets(top: composeMessageView.frame.height - 4, left: 0, bottom: 4, right: 0) for layout reasons. Again, I've set estimatedRowHeight to 44 and rowHeight to UITableViewAutomaticDimension.

Answer 1

func add(_ item: Item) {
// Calculate your `contentOffset` before adding new row
let additionalHeight = tableView.contentSize.height - tableView.frame.size.height
let yOffset = tableView.contentOffset.y
// Update your contentInset to start tableView from bottom of page
updateTableContentInset()
items.append(item)
// Create indexPath and add new row at the end
let indexPath = IndexPath(row: objects.count - 1, section: 0)
tableView.insertRows(at: [indexPath], with: .top)
// Scroll to new added row if you are viewing latest messages otherwise stay at where you are
if yOffset >= additionalHeight {
tableView.scrollToRow(at: indexPath, at: .top, animated: true)
}
}
Here is the method to update contentInset. It will give you the same effect which you were achieving by this CGAffineTransform(scaleX: 1, y: -1)
func updateTableContentInset() {
var contentInsetTop = tableView.frame.size.height - tableView.contentSize.height
if contentInsetTop <= 0 {
contentInsetTop = 0
}
tableView.contentInset = UIEdgeInsets(top: contentInsetTop, left: 0, bottom: 0, right: 0)
}