UICollectionView autosize height

Question

I solved this eventually by fixing all Auto Layout issues, fixing the height of the collection view using a constraint. Then, whenever I know the content has changed I update the value of the constraint using the value collectionView.contentSize.height:

self.verticalLayoutConstraint.constant = self.collectionView.contentSize.height;

Then the collection view is resized properly and it behaves nicely within the overall scrollview. I have updated the GitHub test project with my changes.

To me, doing this by updating the constraint manually instead of being able to tell iOS: "make the frame height of the collection view as large as needed" does not feel right to me, but it's the best I have come up with so far. Please post a better answer if you have one.

It seems to work nicely with a custom UICollectionView class.

class AutoSizedCollectionView: UICollectionView {

    override var contentSize: CGSize {
        didSet {
            invalidateIntrinsicContentSize()
        }
    }

    override var intrinsicContentSize: CGSize {
        layoutIfNeeded()
        return CGSize(width: UIView.noIntrinsicMetric, height: contentSize.height)
    }
}

Set your custom class in the interface builder:

This way you can also set your collection views intrinsic size to 'placeholder' in interface builder to avoid having to set a height constraint.

I hope this helps someone else.

Here's my implementation in Swift 3:

override func sizeThatFits(_ size: CGSize) -> CGSize {
    if (self.superview != nil) {
        self.superview?.layoutIfNeeded()
    }

    return collectionView.contentSize
}

UICollectionViewFlowLayout *flowLayout;
flowLayout = [[UICollectionViewFlowLayout alloc]init];
[flowLayout setScrollDirection:UICollectionViewScrollDirectionVertical];
[flowLayout setMinimumInteritemSpacing:0.0f];
[flowLayout setMinimumLineSpacing:0.0f];
[self.collectionView setPagingEnabled:NO];
[flowLayout setItemSize:CGSizeMake(322.0, 148.0)];  //important to leave no white space between the images
[self.collectionView setCollectionViewLayout:flowLayout];

I found that autolayout in the storyboard is not helping too much. A correct setting for the UICollectionViewFlowLayout for your collectionView is the real help. If you adjust item size with setItemSize, you may get the result you want.