Autolayout Contraints Changes in CollectionViewCell

Question

I am using PureLayout to create the constraints

in cellForItemAtIndexPath

if (!_itemDetails){
            _itemDetails = cell.itemDetails;
            _itemDetailsConstraint = [_itemDetails autoPinEdge:ALEdgeBottom toEdge:ALEdgeBottom ofView:cell.imageView];
        }

and then in scrollDidView

float scrollViewHeight = self.collectionView.frame.size.height;
    float scrollOffset = self.collectionView.contentOffset.y;

    if(_itemDetails){

        if (scrollOffset + scrollViewHeight < CGRectGetMaxY(_frontImageView.frame)){

            _itemDetailsConstraint.constant =  CGRectGetMaxY(_frontImageView.frame) - (scrollOffset + scrollViewHeight);

        }
        else{
            _itemDetailsConstraint.constant = 0;
        }
    }

    [_itemDetails.superview layoutIfNeeded];

eventhough while debugging, I can see that the constraint's constant changed, the view doesn't update to the new location.

I also tried

[self.view layoutIfNeeded]

and

[self.collectionView layoutIfNeeded]

How can I update the view's (_itemDetails, which point to a view in a CollectionViewCell) location?

Answer 1

[collectionView reloadData];

if your contraints is create or update in the collection:cellForItemAtIndexPath:,you can reload all cell.