How can I highlight selected UICollectionView cells? (Swift)

you can use border change on didSelectItemAtIndexPath override event like the below code and assign new settings on the cell.

Swift 3.x:

override func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
    addToList.append(objectsArray[indexPath.row])
    let cell = collectionView.cellForItem(at: indexPath)
    cell?.layer.borderWidth = 2.0
    cell?.layer.borderColor = UIColor.gray.cgColor
}

Here is my solution, and I'm sure it works.

My solution includes 3 highlight effects, UICollectionCell's selectedBackgroundView, cell.contentView.backgroundColor, or your your own specialHighlightedArea; just feel free to choose the one you need, and feel free to add more effects as your App's Designer requires.

How to use? Just inherit BaseCollectionViewCell. If needed, configure in cell's init or collectionView's delegate methods.

If you don't need highlight effect, just find a method named 'shouldHighlightItemAtIndexPath' in UICollectionViewDelegate and return false or just set cell.shouldTintBackgroundWhenSelected = false.

extension UIColor {
    convenience init(rgb: Int, alpha: CGFloat = 1.0) {
        self.init(red: CGFloat((rgb & 0xFF0000) >> 16) / 255.0, green: CGFloat((rgb & 0xFF00) >> 8) / 255.0, blue: CGFloat(rgb & 0xFF) / 255.0, alpha: alpha)
    }
}
/// same with UITableViewCell's selected backgroundColor
private let cellHighlightedColor = UIColor(rgb: 0xD8D8D8) 

class BaseCollectionViewCell: UICollectionViewCell {

    var shouldTintBackgroundWhenSelected = true // You can change default value
    var specialHighlightedArea: UIView?

    // make lightgray background show immediately（on touch）
    // (使灰背景在手指触到 cell 时立即出现)
    override var isHighlighted: Bool { 
        willSet {
            onSelected(newValue)
        }
    }
    // keep lightGray background from selected until unselected 
    // (保留灰背景直至取消选中)
    override var isSelected: Bool { 
        willSet {
            onSelected(newValue)
        }
    }
    func onSelected(_ newValue: Bool) {
        // selectedBackgroundView is defined by UICollectionViewCell
        guard selectedBackgroundView == nil else { return }
        if shouldTintBackgroundWhenSelected {
            contentView.backgroundColor = newValue ? cellHighlightedColor : UIColor.clear
        }
        if let sa = specialHighlightedArea {
            sa.backgroundColor = newValue ? UIColor.black.withAlphaComponent(0.4) : UIColor.clear
        }
    }
}