scrollToRowAtIndexPath always scrolls from the top instead from current offset

Question

In my UITableView I use a method to scroll to the last cell:

WLNetworkClient.sharedClient().createCommentWIthText(commentTextView.text, forItem: item) { error in

    defer {
        UIAlertController.showAlertFromError(error)
    }

    if error == nil {
        self.fetchedResultsController.fetchRequest.fetchLimit += 1
        try! self.fetchedResultsController.performFetch()
        self.tableView.reloadData()
        self.scrollTableViewToBottom()
    }
}

private func scrollTableViewToBottom() {

    tableView.scrollToRowAtIndexPath(NSIndexPath(forRow: fetchedResultsController.fetchedObjects!.count - 1, inSection: 0), atScrollPosition: UITableViewScrollPosition.Bottom, animated: true)
}

but this is not working as it is expected, because ALWAYS table is scrolled from the top even I am on the second cell to last. How to fix this?

thanks for reply, but nothing is gonna work here. The problem is not when, but why it starts from the top? Maybe this is a problem with Xcode 7? — Bartłomiej Semańczyk, Sep 09 '15 at 10:12
Reload should not scroll anywhere unless it cannot maintain the original cells on display.If you comment out the fetch and the scroll to bottom (basically do nothing) does it still scroll to the top? I would strip the code back to see if you can get to a point where reload does not affect position. — Rory McKinnel, Sep 09 '15 at 10:39

score 8 · Answer 1 · answered Jan 12 '17 at 10:03

dosdos answer worked for me in Swift 2 Adding with minor update

Declare the ivar

var heightAtIndexPath = NSMutableDictionary()

in func viewDidLoad()

func viewDidLoad() {
  .... your code
  self.tableView.rowHeight = UITableViewAutomaticDimension
}

Then add the following 2 methods:

override func tableView(tableView: UITableView, estimatedHeightForRowAtIndexPath indexPath: NSIndexPath) -> CGFloat {
   let height = self.heightAtIndexPath.objectForKey(indexPath)
   if ((height) != nil) {
     return CGFloat(height!.floatValue)
   } else {
    return UITableViewAutomaticDimension
   }
 }

override func tableView(tableView: UITableView, willDisplayCell cell: UITableViewCell, forRowAtIndexPath indexPath: NSIndexPath) {
  let height = cell.frame.size.height
  self.heightAtIndexPath.setObject(height, forKey: indexPath)
}

SWIFT 3:

var heightAtIndexPath = NSMutableDictionary()

func tableView(_ tableView: UITableView, estimatedHeightForRowAt indexPath: IndexPath) -> CGFloat {
    let height = self.heightAtIndexPath.object(forKey: indexPath)
    if ((height) != nil) {
        return CGFloat(height as! CGFloat)
    } else {
        return UITableViewAutomaticDimension
    }
}

func tableView(_ tableView: UITableView, willDisplay cell: UITableViewCell, forRowAt indexPath: IndexPath) {
    let height = cell.frame.size.height
    self.heightAtIndexPath.setObject(height, forKey: indexPath as NSCopying)
}

You are my saviour, I did not expect the automatic dimensioning of the cells to cause this issue. Thanks! — Swift Rabbit, Apr 18 '17 at 14:02

score 1 · Answer 2 · answered May 11 '18 at 12:21

Extending ZaEeM ZaFaR great answer:

Objective C

NSMutableDictionary *heightAtIndexPath;
heightAtIndexPath = [[NSMutableDictionary alloc] init];

- (CGFloat)tableView:(UITableView *)tableView estimatedHeightForRowAtIndexPath:(NSIndexPath *)indexPath {
    NSNumber *height = [heightAtIndexPath objectForKey:indexPath];
    if(height) {
        return height.floatValue;
    } else {
        return UITableViewAutomaticDimension;
    }
}

- (void)tableView:(UITableView *)tableView willDisplayCell:(UITableViewCell *)cell forRowAtIndexPath:(NSIndexPath *)indexPath {
    [heightAtIndexPath setObject:@(cell.frame.size.height) forKey:indexPath];
}

score 0 · Answer 3 · answered Sep 09 '15 at 10:01

I think the problem is you scroll before the tableView update (by self.tableView.reloadData()). Try to delay the scrolling:

     dispatch_async(dispatch_get_main_queue()) {
         self.scrollTableViewToBottom()
    }

Or force the tableView to update:

    self.tableView.reloadData()
    self.tableView.layoutIfNeeded()
    self.scrollTableViewToBottom()

score 0 · Answer 4 · edited May 23 '17 at 12:02

0

This issue is covered here: How to tell when UITableVIew has completed ReloadData?

Change your code to:

self.tableView.reloadData()
self.tableView.layoutIfNeeded()
self.scrollTableViewToBottom()

The layoutIfNeeded forces the table reload to happen immediately. All explained in the link.

edited May 23 '17 at 12:02

Community

1
1

answered Sep 09 '15 at 10:08

Rory McKinnel

7,936
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score 0 · Answer 5 · answered Aug 24 '17 at 10:53

To be swiftier I would simplify the Swift 3 version introduced above:

    var heightAtIndexPath = [IndexPath: CGFloat]()

    func tableView(_ tableView: UITableView, estimatedHeightForRowAt indexPath: IndexPath) -> CGFloat {
        if let height = self.heightAtIndexPath[indexPath] {
            return height
        }
        return UITableViewAutomaticDimension
    }

    func tableView(_ tableView: UITableView, willDisplay cell: UITableViewCell, forRowAt indexPath: IndexPath) {
        let height = cell.frame.size.height
        self.heightAtIndexPath[indexPath] = height
    }

scrollToRowAtIndexPath always scrolls from the top instead from current offset

5 Answers5