UICollectionViewFlowLayout

UICollectionViewFlowLayout

//In UICollectionViewCell subclass implementation
- (UICollectionViewLayoutAttributes *)preferredLayoutAttributesFittingAttributes:(UICollectionViewLayoutAttributes *)layoutAttributes {
    layoutAttributes.size = CGSizeMake(layoutAttributes.frame.size.width, layoutAttributes.frame.size.height);
    return layoutAttributes;
}

//In your view controller (containing the UICollectionView).
    //In @interface
    @property (nonatomic, strong) UICollectionViewFlowLayout *layout;

    //In viewDidLoad
    self.layout = [[UICollectionViewFlowLayout alloc] init];
    [self.collectionView setCollectionViewLayout:self.layout];

    //In viewWillAppear
    self.layout.estimatedItemSize = CGSizeMake(160.0, 44.0); //E.g. for half-width cells.