swift collection view deselects item when scroll off screen

class MyViewController {

    var selectedIndexes = [IndexPath]()

    func cellForItem(indexPath) {
       cell.isSelected =  selectedIndexes.contains(indexPath)
    }

    func didSelectCell(indexPath) {
        if selectedIndexes.contains(indexPath) {
            selectedIndexes.remove(indexPath)
        } else if selectedIndexes.count < limiit {
            selectedIndexes.append(indexPath)
        }
    }
}