How can a get the auto layout size of the UICollectionViewCells in iOS 8? (systemLayoutSizeFittingSize returns size with zero height in iOS 8)

Question

Since iOS 8 [UIColletionViewCell systemLayoutSizeFittingSize:UILayoutFittingCompressedSize] returns a size with height of 0.

Here\'s what the code

Answer 1

We're using a work-around for now, copied below. Hopefully, these issues will be resolved before iOS 8 release and we can remove this. (The kludge assumes knowledge of Apple's implicit contentView behavior, and we have to hack IB outlet references to any constraints we transfer.)

We notice they're also removing all autoresizingMasks from storyboards/NIBs during upgrade, which makes sense given it's supposed to be auto-layout, but collection views still throwback to springs & struts. Perhaps this has been overlooked in the purge?

--Dan

/**
 Kludge around cell sizing issues for iOS 8 and deployment to iOS 7 when compiled for 8.  Call this on the collection view cell before it is used, such as in awakeFromNib.  Because this manipulates top-level constraints, any references to such initial constraints, such as from IB outlets, will be invalidated.

 Issue 1: As of iOS 8 Beta 5, systemLayoutSizeFittingSize returns height 0 for a UICollectionViewCell.  In IB, cells have an implicit contentView, below which views placed in IB as subviews of the cell are actually placed.  However, constraints set between these subviews and its superview are placed on the cell, rather than the contentView (which is their actual superview).  This should be OK, as a constraint among items may be placed on any common ancestor of those items, but this is not playing nice with systemLayoutSizeFittingSize.  Transferring those constraints to be on the contentView seems to fix the issue.

 Issue 2: In iOS 7, prior to compiling against iOS 8, the resizing mask of the content view was being set by iOS to width+height.  When running on iOS 7 compiled against iOS 8 Beta 5, the resizing mask is None, resulting in constraints effecting springs for the right/bottom margins.  Though this starts out the contentView the same size as the cell, changing the cell size, as we do in the revealing list, is not tracked by changing it's content view.  Restore the previous behavior.

 Moving to dynamic cell sizing in iOS 8 may circumvent this issue, but that remedy isn't available in iOS 7.
*/
+ (void)kludgeAroundIOS8CollectionViewCellSizingIssues:(UICollectionViewCell *)cell {

    // transfer constraints involving descendants on cell to contentView
    UIView *contentView = cell.contentView;
    NSArray *cellConstraints = [cell constraints];
    for (NSLayoutConstraint *cellConstraint in cellConstraints) {
        if (cellConstraint.firstItem == cell && cellConstraint.secondItem) {
            NSLayoutConstraint *parallelConstraint = [NSLayoutConstraint constraintWithItem:contentView attribute:cellConstraint.firstAttribute relatedBy:cellConstraint.relation toItem:cellConstraint.secondItem attribute:cellConstraint.secondAttribute multiplier:cellConstraint.multiplier constant:cellConstraint.constant];
            parallelConstraint.priority = cellConstraint.priority;
            [cell removeConstraint:cellConstraint];
            [contentView addConstraint:parallelConstraint];
        } else if (cellConstraint.secondItem == cell && cellConstraint.firstItem) {
            NSLayoutConstraint *parallelConstraint = [NSLayoutConstraint constraintWithItem:cellConstraint.firstItem attribute:cellConstraint.firstAttribute relatedBy:cellConstraint.relation toItem:contentView attribute:cellConstraint.secondAttribute multiplier:cellConstraint.multiplier constant:cellConstraint.constant];
            parallelConstraint.priority = cellConstraint.priority;
            [cell removeConstraint:cellConstraint];
            [contentView addConstraint:parallelConstraint];
        }
    }

    // restore auto-resizing mask to iOS 7 behavior
    contentView.autoresizingMask = UIViewAutoresizingFlexibleWidth | UIViewAutoresizingFlexibleHeight;
    [cell setNeedsUpdateConstraints];
    [cell updateConstraintsIfNeeded];
}