How maintain scroll position?

[educosta]

How can I still scroll position when I load new messages?

If disabled automaticallyScrollsToMostRecentMessage scroll to up, if enabled scroll to down.

Thank you

[dim0v]

Hi, @educosta!
You can use UIScrollView contentOffset and contentSize properties.

Before loading a new bunch of messages save your current y-offset (but counting from the bottom, not from the top). I.e.

CGFloat oldOffset = self.collectionView.contentSize.height - self.collectionView.contentOffset.y

After that, load new messages to dataSource, call [self.collectionView reloadData] and [self.collectionView layoutIfNeeded] and set collectionView's contentOffset to the one you've previously saved (remember that it's "reversed"):

self.collectionView.contentOffset = CGPointMake(0.0, self.collectionView.contentSize.height - oldOffset);

[jessesquires]

thanks for the answer @dim0v!

[educosta]

Hi @dim0v

Works for you? I tried on demo project but not works :(

[dim0v]

Here is the code I am using in my current project (a bit simplified and cleared from unrelated things). It works fine.

- (void) loadHistory {
    CGFloat oldOffsetReversed = self.collectionView.contentSize.height - self.collectionView.contentOffset.y;

    NSUInteger pageSize = [self fetchNextPage]; //reloadData is called inside
    [self.view layoutIfNeeded];

    CGFloat offset = self.collectionView.contentSize.height - oldOffsetReversed;

    self.collectionView.contentOffset = CGPointMake(self.collectionView.contentOffset.x, offset);
}

[dim0v]

Also, if message loading is asynchronous, this should be done inside the completion handler.

If still doesn't work for you, please, post your code somwhere, i'll try to figure out why :)

Btw, I assumed you are loading messages on the top. If new messages are added to the bottom, then setting automaticallyScrollsToMostRecentMessage to NO should be enough to preserve scroll position.

[educosta]

Hi @dim0v

Now works, I missing [self.view layoutIfNeeded]; after reload

You're the best!

[mitchellporter]

@dim0v works perfectly even on iOS 9 ;)

[bpisano]

I have this issue too and I've tried the layoutIfNeeded. But with a lot of cells and self sizing, it completely freeze the UI.