Swift 3：以编程方式调整UICollectionViewCell的大小会导致单元格重叠

我正在尝试创建一个UICollectionView彼此下面的3个单元格。这工作正常。当我触摸一个单元格时，该单元格应该展开，其他单元格应该折叠到特定高度。也工作得很好。

我无法解决的问题；当我点击一个单元格时，它会像我想要的那样扩展；它与这个下面的那个重叠。下面的那个不会向下移动，以便为该单元格增加新的空间。

我怎样才能解决这个问题？

到目前为止，这是我与UICollectionView和相关的UICollectionViewCell

/**
 * Tempory 3 items
 */
func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
    return 3
}

/**
 * Defining the cells
 */
func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {

    let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "cell", for: indexPath) as! LicenseplateCollectionViewCell

    cell.backgroundColor = .white
    cell.layer.cornerRadius = 4

    if(indexPath.row > 0){
        cell.carStack.isHidden = true
    }

    return cell
}


/**
 * Initial size
 */
func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {
    // The first cell always start expanded with an height of 300
    if(indexPath.row == 0){
        return CGSize(width: collectionView.bounds.size.width, height: 300)
    }else{
        // The others start with an height of 80
        return CGSize(width: collectionView.bounds.size.width, height: 80)
    }
}

/**
 * This functio shoud be handling everything like an accordeon system.
 * When I touch one cell, the others should collapse.
 */
func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {

    // Animate resize of cell after tapping
    UIView.animate(withDuration: 0.2, animations: {
        // For now I have 3 cells, which I will loop
        for i in 0...2{
            // If this is the active cell (I just tapped on) ...
            if(indexPath.row == i){
                let cell = collectionView.cellForItem(at: indexPath) as! LicenseplateCollectionViewCell
                // This cell is expanded already, collapse it
                if(cell.frame.size.height > 200){
                    cell.carStack.isHidden = true
                    cell.frame.size = CGSize(width: collectionView.bounds.size.width, height: 80)
                }else{
                    // Open up this cell
                    cell.carStack.isHidden = false
                    cell.frame.size = CGSize(width: collectionView.bounds.size.width, height: 300)
                }
            }else{
                // Other cells besides the one I just tapped, will be collapsed
                print(indexPath.row, indexPath.section)
                let customPath = IndexPath(row: i, section: 0)
                print(customPath.row, customPath.section)
                let cell = collectionView.cellForItem(at: customPath) as! LicenseplateCollectionViewCell
                cell.carStack.isHidden = true
                cell.frame.size = CGSize(width: collectionView.bounds.size.width, height: 80)
            }
        }
    })

}