Q:

UICollectionViewDelegateFlowLayout is not changing cell bounds

I have problem with setting shadow path for UICollectionViewCell which has a relative width to collectionView bounds.
Im using storyboard constraints, setting up shadow in AwakeFromNib method and resizing cell with sizeForItemAt method
 //cell awakeFromNib    
    override func awakeFromNib() {

    self.backgroundColor = UIColor.white

    self.contentView.layer.cornerRadius = 2.0
    self.contentView.layer.borderWidth = 1.0
    self.contentView.layer.borderColor = UIColor.clear.cgColor
    self.contentView.layer.masksToBounds = true

    self.layer.shadowColor = UIColor.black.cgColor
    self.layer.shadowOffset = CGSize(width: 0, height: 2.0)
    self.layer.shadowRadius = 2.0
    self.layer.shadowOpacity = 0.5
    self.layer.masksToBounds = false
    self.layer.shadowPath = UIBezierPath(roundedRect: self.bounds, cornerRadius: self.contentView.layer.cornerRadius).cgPath
}

// collection view method
func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {

    let height: CGFloat = 288

    return CGSize(width: collectionView.bounds.size.width-20, height: height)
}

Cell bounds:
AwakeFromNib method - (307.0, 288.0)
Expected - (300.0, 288.0)
What is the problem?

A:

The problem is that the bounds/frame are changing if your cell is layouted.
Add this to your collectionViewCell - subclass:
    override func layoutSubviews() {
    super.layoutSubviews()
        self.layer.shadowPath = UIBezierPath(roundedRect: self.bounds,  cornerRadius: self.contentView.layer.cornerRadius).cgPath
    }

