展开和折叠UICollectionViewController中选定部分中的单元格

Question

当单击节标题但所有标题都在扩展而不是所选标题时，我一直在尝试折叠和展开collectionView中的单元格。 这是我的代码

class ExampleHomeController: UICollectionViewController, UICollectionViewDelegateFlowLayout {

var expandedRow: Bool = false
var section: Int!

let postCellId = "postCellId"
let headerCellId = "headerCellId"

override func viewDidLoad() {
    super.viewDidLoad()

    collectionView.delegate = self
    collectionView.dataSource = self

    collectionView.backgroundColor = UIColor.init(r: 220, g: 214, b: 214)

    collectionView.register(PostCell.self, forCellWithReuseIdentifier: postCellId)
    collectionView.register(HeaderCell.self, forSupplementaryViewOfKind: UICollectionView.elementKindSectionHeader, withReuseIdentifier: headerCellId)

}

override func numberOfSections(in collectionView: UICollectionView) -> Int {
    return 4
}


override func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
    return 3
}

override func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
    let cell = collectionView.dequeueReusableCell(withReuseIdentifier: postCellId, for: indexPath)
    return cell
}

override func collectionView(_ collectionView: UICollectionView, viewForSupplementaryElementOfKind kind: String, at indexPath: IndexPath) -> UICollectionReusableView {
    let header = collectionView.dequeueReusableSupplementaryView(ofKind: kind, withReuseIdentifier: headerCellId, for: indexPath) as! HeaderCell
    header.downArrowBtn.addTarget(self, action: #selector(showCells), for: .touchUpInside)
    return header

}

@objc func showCells() {
    if expandedRow == false {
        expandedRow = true
    }else {
        expandedRow = false
    }
    collectionView.reloadData()
}


func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {
    if expandedRow == true {
        return CGSize(width: view.frame.width - 24, height: 280)
    } else {
        return CGSize(width: view.frame.width - 24, height: 0)
    }
}

}

这是我的帖子单元格

class PostCell: UICollectionViewCell {
override init(frame: CGRect) {
    super.init(frame: frame)

    setupViews()
}

required init?(coder aDecoder: NSCoder) {
    fatalError("init(coder:) has not been implemented")
}

let postImage: UIImageView = {
    let view = UIImageView()
    view.image = #imageLiteral(resourceName: "one")
    return view
}()


func setupViews() {

    backgroundColor = .white

    addSubview(postImage)

    postImage.anchor(top: contentView.topAnchor, leading: nil, bottom: contentView.bottomAnchor, trailing: nil, padding: .init(top: 20, left: 0, bottom: 0, right: 0), size: .init(width: 70, height: 0))
    postImage.centerXAnchor.constraint(equalTo: contentView.centerXAnchor).isActive = true
}

}

这是我的HeaderCell

class HeaderCell: UICollectionViewCell  {

var expandedRow: Bool!

override init(frame: CGRect) {
    super.init(frame: frame)
    backgroundColor = UIColor.init(r: 220, g: 214, b: 214)
    setupViews()
}

required init?(coder aDecoder: NSCoder) {
    fatalError("init(coder:) has not been implemented")
}

let headerImage: UIImageView = {
    let view = UIImageView()
    view.image = #imageLiteral(resourceName: "facebook")
    return view
}()

let headerLabel: UILabel = {
    let label = UILabel()
    label.text = "Posts By Network"
    return label
}()

let downArrowBtn: UIButton = {
    let button = UIButton()
    button.setImage(#imageLiteral(resourceName: "downarrow"), for: .normal)
    button.imageView?.contentMode = .scaleAspectFit
    return button
}()

func setupViews() { 
    addSubview(headerImage)
    addSubview(headerLabel)
    addSubview(downArrowBtn)

    headerImage.anchor(top: contentView.topAnchor, leading: contentView.leadingAnchor, bottom: nil, trailing: nil, padding: .init(top: 8, left: 12, bottom: 0, right: 0), size: .init(width: 30, height: 30))
    headerLabel.anchor(top: headerImage.topAnchor, leading: headerImage.trailingAnchor, bottom: nil, trailing: nil, padding: .init(top: 2, left: 20, bottom: 0, right: 0))
    headerLabel.centerYAnchor.constraint(equalTo: headerImage.centerYAnchor).isActive = true
    downArrowBtn.anchor(top: headerLabel.topAnchor, leading: headerLabel.trailingAnchor, bottom: nil, trailing: contentView.trailingAnchor, padding: .init(top: 0, left: 0, bottom: 0, right: 12), size: .init(width: 20, height: 20))

}

}

单击标题时，所有单元格都在扩展，但是我只想扩展和折叠所选部分，我该怎么做。我是新手，过去几周一直在尝试这种方法。 谢谢