Detect the current top cell in a UITableView after scrolling

Question

a simple question but I don't seem to have the right terminology to search Stackoverflow by it.

I have a UITableView with no sections, the user can scroll up and down a long list of data (rows) presented inside this tableview.

Question: how can I detect the most top cell row number after the user scrolled. (for example, if the user is scrolling 30 cells down, the top cell after the scroll is = 30)

score 77 · Accepted Answer · edited Sep 21 '17 at 06:43

77

You could try using UITableView's -indexPathsForVisibleRows or -indexPathForRowAtPoint.

For example, let's say that you want to print the indexPath of the topmost visible cell, when you stop dragging your table. You could do something like this:

- (void)scrollViewDidEndDragging:(UIScrollView *)scrollView willDecelerate:(BOOL)decelerate{
    NSIndexPath *firstVisibleIndexPath = [[self.tableView indexPathsForVisibleRows] objectAtIndex:0];
    NSLog(@"first visible cell's section: %i, row: %i", firstVisibleIndexPath.section, firstVisibleIndexPath.row);
}

For Swift 3.0

let topVisibleIndexPath:IndexPath = self.tableView.indexPathsForVisibleRows![0]

edited Sep 21 '17 at 06:43

Patel Jigar

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answered Nov 24 '11 at 15:43

phi

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I would sort the array as there's nothing (as far as I can see) in the documentation that says the index paths are sorted in ascending order. – jbat100 Nov 24 '11 at 15:52
1

It's a different question, but check `tableView scrollToRowAtIndexPath` – phi Nov 24 '11 at 16:06
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Beware, `[self.tableView indexPathsForVisibleRows]` could be empty when the user scrolls a table view with bouncing enabled like a chick on speed. So be sure to check whether the method returned at least 1 index path. – Thomas Kekeisen Apr 14 '14 at 16:19
"indexPathsForVisibleRows" returns invisible rows as well. Any better approach? – Dipak Mar 01 '22 at 07:45

score 32 · Answer 2 · answered Nov 24 '11 at 15:49

32

You get the index paths for the visible rows

NSArray* indexPaths = [tableView indexPathsForVisibleRows];

Then sort using compare:

NSArray* sortedIndexPaths = [indexPaths sortedArrayUsingSelector:@selector(compare:)];

Then get the first element's row

NSInteger row = [(NSIndexPath*)[sortedIndexPaths objectAtIndex:0] row];

answered Nov 24 '11 at 15:49

jbat100

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This solution works on `UICollectionView`s along with `UITableView`s – aytunch Nov 29 '15 at 19:34

mathema · Answer 3 · 2018-04-05T21:23:51.390

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This is the Swift 3+ code:

override func scrollViewDidEndDragging(_ scrollView: UIScrollView, willDecelerate decelerate: Bool) {
    let firstVisibleIndexPath = self.tableView.indexPathsForVisibleRows?[0]
    print("First visible cell section=\(firstVisibleIndexPath?.section), and row=\(firstVisibleIndexPath?.row)")
}

edited Apr 05 '18 at 21:23

answered Dec 08 '16 at 06:35

mathema

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score 0 · Answer 4 · edited Sep 19 '20 at 03:09

0

In Swift 4:

func tableView(_ tableView: UITableView, willDisplay cell: UITableViewCell, forRowAt indexPath: IndexPath) {
    let firstVisibleIndexPath = self.tableview.indexPathsForVisibleRows?[0]
    print("top visible cell section  is \([firstVisibleIndexPath!.section])")
}

edited Sep 19 '20 at 03:09

ib.

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answered Feb 21 '20 at 11:11

Radhe Yadav

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Detect the current top cell in a UITableView after scrolling

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