The content of my UICollectionView flows in horizontal direction. Height of items are fixed but width of each are dynamic based on the length of text. For this example I am using only UILabel in my UICollectionViewCell. My UICollectionViewCell is custom xib.

These are the constraints I have applied to UILabel:

• Leading : 0
• Trailing : 0
• Top : 0
• Height : 44

I have applied height constraint because I do not want height calculation processed for any intentional or non-intentional line breaks. I also make sure that number of lines in UILabel is 1 for my purpose because I do not want line breaks and ensures my layout lays out in horizontal list of one liners.

I have to set estimated size to automatic on layout:

((UICollectionViewFlowLayout *)collectionView.collectionViewLayout).estimatedItemSize = UICollectionViewFlowLayoutAutomaticSize;

It works as long I am not building with iOS 12 base sdk. The output that I see looks like auto layout constraints are all ignored when building with iOS 12. Why? I have no detailed insight on this but I do have a workaround.

// The Workaround

I mentioned that I am using custom xib and subclass. Inside - (void)awakeFromNib I explicitly activate the constraints again.

- (void)awakeFromNib {
    [super awakeFromNib];

    if (@available(iOS 12.0, *)) {
        self.contentView.translatesAutoresizingMaskIntoConstraints = NO;

        NSLayoutConstraint *leftConstraint = [self.contentView.leftAnchor constraintEqualToAnchor:self.leftAnchor constant:8];
        NSLayoutConstraint *rightConstraint = [self.contentView.rightAnchor constraintEqualToAnchor:self.rightAnchor constant:8];
        NSLayoutConstraint *topConstraint = [self.contentView.topAnchor constraintEqualToAnchor:self.topAnchor constant:0];
constraintEqualToAnchor:self.bottomAnchor constant:0];
        NSLayoutConstraint *heightConstraint = [NSLayoutConstraint constraintWithItem:self.historyItemLabel
                                     attribute:NSLayoutAttributeHeight
                                     relatedBy:NSLayoutRelationEqual
                                        toItem:nil
                                     attribute: NSLayoutAttributeNotAnAttribute
                                    multiplier:1
                                                                             constant:44];
        [NSLayoutConstraint activateConstraints:@[leftConstraint, rightConstraint, topConstraint, heightConstraint]];
    }
}

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