How to align a UITableViewCell at the bottom of a UITableView?

Question

When you insert your first UITableViewCells insertRowsAtIndexPaths:withRowAnimation:, it usually appears at the top UITableView. The opposite happens in the Periscope app - the first inserted cell is aligned at the bottom. As you enter new cells, the old cells move up in the table. How is this achieved?

Answer 1

If you're curious how I did this in an iOS Periscope app, it's actually pretty simple ...

TL; DR; , . , , .

:

- (UIView *)tableView:(UITableView *)tableView viewForHeaderInSection:(NSInteger)section
{
    UIView *headerView = [[UIView alloc] initWithFrame:CGRectZero];
    headerView.userInteractionEnabled = NO; // all touches within this space must go through to the video layer

    return headerView;   // empty header above chat, so messages flow in from bottom
}

- (CGFloat)tableView:(UITableView *)tableView heightForHeaderInSection:(NSInteger)section
{
    return self.tableView.frame.size.height;            // empty header above chat, so messages flow in from bottom
}

( _messages. reloadData UITableViewController). :

- (void)scrollTableToBottom
{
    if (!self.isViewLoaded || _messages.count == 0)
        return;

    CGFloat offsetY = self.tableView.contentSize.height - self.tableView.frame.size.height + self.tableView.contentInset.bottom;

    [UIView animateWithDuration:0.33
            delay:0
            options:UIViewAnimationOptionCurveEaseOut | UIViewAnimationOptionAllowUserInteraction
            animations:^{
                [self.tableView setContentOffset:CGPointMake(0, offsetY) animated:NO];
            }
            completion:nil];
}

, . / , . , , .: -)

Answer 2

insertRowsAtIndexPath, .

[self.tableView insertRowsAtIndexPaths:@[[NSIndexPath indexPathForRow:self.posts.count-1 inSection:0]] withRowAnimation:UITableViewRowAnimationBottom];
[self.tableView scrollToRowAtIndexPath:indexPath atScrollPosition:UITableViewScrollPositionBottom animated:YES];

, .

, .

Answer 3

Swift 4 versions of Aaron Wasserman's answer.

func tableView(_ tableView: UITableView, viewForHeaderInSection section: Int) -> UIView? {
    let headerView = UIView(frame: .zero)
    headerView.isUserInteractionEnabled = false
    return headerView
}

// Added logic to avoid blank space at the top
func tableView(_ tableView: UITableView, heightForHeaderInSection section: Int) -> CGFloat {
    return tableView.frame.size.height - CGFloat(messages.count * cellHeight)
}

 func scrollToBottom(animated: Bool) {
    if isViewLoaded && messages.count > 0 {

        let offset = tableView.contentSize.height - tableView.frame.size.height + tableView.contentInset.bottom

        UIView.animate(withDuration: 0.33, delay: 0, options: [.curveEaseOut, .allowUserInteraction], animations: {
            self.tableView.setContentOffset(CGPoint(x: 0, y: offset), animated: animated)
        }, completion: nil)
    }
}

The scrollToBottom method needs to be called after tableView.reloadData ()