Resize UITableView height, and keep scrolled at bottom - ios

Question

Im trying to resize the tableview's height with a animation, it works fine by animating the tableview's frame.size.height.
The problem is, i have a tableview that is 200px height and scrolled to the bottom, i want to animate this to 100px, i run a simple
[UIView animateWithDuration:0.245f animations:^{
CGRect frame = tableview.frame;
frame.size.height = 100.f;
tableview.frame = frame;
}];
this works fine, but after i resized it it is no longer scrolled to the bottom of the tableview. i want the tableview to always be scrolled at the bottom while animating. i tried alot of differnet things like calling
[tablview scrollToRowAtIndexPath:indexPath atScrollPosition:UITableViewScrollPositionTop animated:YES];
right before/after i start the resize animation, but i have not managed to get them to sync 100%. Is there a way to resize the tableview while the bottom of the tableview displays the last element of the scrollview.

Answer 1

I found a solution for my problem, there might very well be a better solution but this actually works quite well :)
Before i start animating i see if the contentSize.height is larger than the target height, if so i do following:
if (mMessages.contentSize.height > 150.f)
{
CGFloat expandedOffsetY = 52.f;
CGFloat collapsedBottomOffset = (150.f + 18.f);
CGFloat expandedBottomOffset = (MIN(320.f, mMessages.contentSize.height) + expandedOffsetY);
tableFrame.origin.y = (collapsedBottomOffset - expandedBottomOffset) + expandedOffsetY;
}
else
{
tableFrame.origin.y = 18.f;
tableFrame.size.height = 150.f;
}
this will put the tableview in a minus origin.y, then i have wrapped the tableview inside a "parent" uiview with clip sub views = YES.
Then i have a "completed" animation block that "resets" to the target values.
CGRect tableFrame = mMessages.frame;
tableFrame.origin.y = 18.f;
tableFrame.size.height = 150.f;
mMessages.frame = tableFrame;
if (mMessages.contentSize.height > tableFrame.size.height)
{
float contentOffsetY = mMessages.contentSize.height - tableFrame.size.height;
mMessages.contentOffset = CGPointMake(0.0f, contentOffsetY);
}

Answer 2

Try updating the contentOffset of the table view as you animate the frame.
[UIView animateWithDuration:0.245f animations:^{
CGRect frame = tableview.frame;
frame.size.height = 100.f;
tableview.frame = frame;
float contentOffsetY = tableview.contentSize - tableview.frame.size.height;
tableview.contentOffset = CGPointMake(0, contentOffsetY);
}];

Answer 3

[UIView animateWithDuration:0.245f animations:^{
CGRect frame = tableview.frame;
frame.size.height = 100.f;
tableview.frame = frame;
} completion:^(BOOL finished) {
// Find your last indexpath
[tablview scrollToRowAtIndexPath:indexPath atScrollPosition:UITableViewScrollPositionTop animated:YES];
} ];

Answer 4

Scrolling the tableview to the bottom in the animation block was working for me, with one little twist: when I reduced the hight of the tableView I called scrollToIndexPath without animating, and when I expand the tableView I called the scrollToIndexPath with animation.
UIView.animate(withDuration: 0.25) { [weak self] in
guard let strongSelf = self
else { return }
// ...
// updateConstraints
// ...
strongSelf.view.layoutIfNeeded()
if reduceSize {
tableView.scrollToLastRow(animated: false)
} else {
tableView.scrollToLastRow(animated: true)
}
}
Extension for UITableView
extension UITableView {
func scrollToLastRow(animated: Bool) {
let lastSection = numberOfSections-1
let lastRow = numberOfRows(inSection: lastSection)-1
let lastIndexPath = IndexPath(row: lastRow, section: lastSection)
scrollToRow(at: lastIndexPath, at: .bottom, animated: animated)
}
}