Keep uitableview static when inserting rows at the

Question

I have a tableView that I'm inserting rows into at the top.

Whilst I'm doing this I want the current view to stay completely still, so the rows only appear if you scroll back up.

I've tried saving the current position of the underlying UIScrollview and resetting the position after the rows have been inserted but this results in a judder, up and down, although it does end up back in the same place.

Is there a good way of achieving this ?

Update: I am using beginUpdate, then insertRowsAtIndexPath, endUpdates. There is no reloadData call.

scrollToRowAtIndexPath jumps to the top of the current cell (saved before adding rows).

The other approach I tried, which ends up in exactly the right pace, but with a judder is.

save tableView currentOffset. (Underlying scrollView method)
Add rows (beginUpdates,insert...,endUpdates) 
reloadData ( to force a recalulation of the scrollview size )
Recalculate the correct new offset from the bottom of the scrollview
setContentOffset (Underlying scrollview method)

Trouble is the reloadData causes the scrollview/tableview to start scrolling briefly, then the setContentOffset returns it to the correct place.

Is there a way of getting a tableView to work out it's new size without starting display ?

Wrapping the whole thing in a beginAnimation commitAnimation doesn't help much either.

Update 2: This can clearly be done - see the offical twitter app for one when you pull down for updates.

Answer 1

I want add additional condition. If your code in iOS11 or more, you need do like below;

In iOS 11, table views use estimated heights by default. This means that the contentSize is just as estimated value initially. If you need to use the contentSize, you’ll want to disable estimated heights by setting the 3 estimated height properties to zero:

tableView.estimatedRowHeight = 0 tableView.estimatedSectionHeaderHeight = 0 tableView.estimatedSectionFooterHeight = 0

Answer 2

Simple solution to disable animations

func addNewRows(indexPaths: [NSIndexPath]) {
    let addBlock = { () -> Void in
        self.tableView.beginUpdates()
        self.tableView.insertRowsAtIndexPaths(indexPaths, withRowAnimation: .None)
        self.tableView.endUpdates()
    }

    tableView.contentOffset.y >= tableView.height() ? UIView.performWithoutAnimation(addBlock) : addBlock()
}

Answer 3

@Dean's way of using an image cache is too hacky and I think it destroys the responsiveness of the UI.

One proper way: Use a UITableView subclass and override -setContentSize: in which you can by some means calculate how much the table view is pushed down and offset that by setting contentOffset.

This is a simplest sample code to handle the simplest situation where all insertions happen at the top of table view:

@implementation MyTableView

- (void)setContentSize:(CGSize)contentSize {
        // I don't want move the table view during its initial loading of content.
    if (!CGSizeEqualToSize(self.contentSize, CGSizeZero)) {
        if (contentSize.height > self.contentSize.height) {
            CGPoint offset = self.contentOffset;
            offset.y += (contentSize.height - self.contentSize.height);
            self.contentOffset = offset;
        }
    }
    [super setContentSize:contentSize];
}

@end

Answer 4

There's really no need to sum up all rows height, the new contentSize after reloading the table is already representing that. So all you have to do is calculate the delta of contentSize height and add it to the current offset.

    ...
    CGSize beforeContentSize = self.tableView.contentSize;
    [self.tableView reloadData];
    CGSize afterContentSize = self.tableView.contentSize;

    CGPoint afterContentOffset = self.tableView.contentOffset;
    CGPoint newContentOffset = CGPointMake(afterContentOffset.x, afterContentOffset.y + afterContentSize.height - beforeContentSize.height);
    self.tableView.contentOffset = newContentOffset;
    ...

Answer 5

Everyone loves copy and pasting code examples, so here's an implementation of Andrey Z.'s answer.

This is in my delegateDidFinishUpdating:(MyDataSourceDelegate*)delegate method

if (self.contentOffset.y <= 0)
{
    [self beginUpdates];
    [self insertRowsAtIndexPaths:insertedIndexPaths withRowAnimation:insertAnimation];
    [self endUpdates];
}
else
{
    CGPoint newContentOffset = self.contentOffset;
    [self reloadData];

    for (NSIndexPath *indexPath in insertedIndexPaths)
        newContentOffset.y += [self.delegate tableView:self heightForRowAtIndexPath:indexPath];

    [self setContentOffset:newContentOffset];

    NSLog(@"New data at top of table view");
}

The NSLog at the bottom can be replaced with a call to show a view that indicated there's fresh data.

Answer 6

had the same problem and found a solution.

    save tableView currentOffset. (Underlying scrollView method)
    //Add rows (beginUpdates,insert...,endUpdates) // don't do this!
    reloadData ( to force a recalulation of the scrollview size )
    add newly inserted row heights to contentOffset.y here, using tableView:heightForRowAtIndexPath:
    setContentOffset (Underlying scrollview method)

like this:

- (CGFloat) firstRowHeight
{
    return [self tableView:[self tableView] heightForRowAtIndexPath:[NSIndexPath indexPathForRow:0 inSection:0]];
}

...
CGPoint offset = [[self tableView] contentOffset];
[self tableView] reloadData];
offset.y += [self firstRowHeight];
if (offset.y > [[self tableView] contentSize].height) {
    offset.y = 0;
}
[[self tableView] setContentOffset:offset];
...

works perfectly, without glitches.