Swift 以编程方式使UIView居中，而不影响UIKit中其他UI类的位置

我想通过修改约束属性(如topAnchor)将UIView boardGame: UICollectionView的位置移动到屏幕中央，但我对它所做的任何操作似乎都会影响它内部的内容.我还定义了UICollectionViewCell模型，这样我就可以将boardGame中的单元注册为"uinique".

import UIKit

class BoardViewController: UIViewController {

    private let boardGame: UICollectionView = {
        let layout = UICollectionViewFlowLayout()
        let board = UICollectionView(frame: .zero, collectionViewLayout: layout)
        board.allowsSelection =  true
        board.register(CustomCollectionViewCell.self, forCellWithReuseIdentifier: "unique")
        board.translatesAutoresizingMaskIntoConstraints = false
        return board
    }()
    
    override func viewDidLoad() {
        super.viewDidLoad()
        view.addSubview(boardGame)
        boardGame.backgroundColor = .systemGray2
        
        boardGame.frame = view.bounds
        
        let margin: CGFloat = 20
        NSLayoutConstraint.activate([
               
            boardGame.topAnchor.constraint(equalTo: view.topAnchor, constant: margin),
            boardGame.centerXAnchor.constraint(equalTo: view.centerXAnchor),
                   boardGame.centerYAnchor.constraint(equalTo: view.centerYAnchor),
            
                  
                   boardGame.widthAnchor.constraint(equalTo: view.widthAnchor, constant: -20),
                   boardGame.heightAnchor.constraint(equalTo: view.widthAnchor, constant: -20),
               ])
        
       
        
        boardGame.delegate = self
        boardGame.dataSource = self
        
    }
    
    init() {
           super.init(nibName: nil, bundle: nil)
       }
       required init?(coder: NSCoder) {
           fatalError("init(coder:) has not been implemented")
       }
}

extension BoardViewController: UICollectionViewDelegateFlowLayout, UICollectionViewDataSource {
    
    
    func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        return 9
    }
    
    
    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "unique", for: indexPath) as! CustomCollectionViewCell

              
              let chessRow = indexPath.row / 3
              if chessRow % 2 == 0 {
                  if indexPath.row % 2 == 0 {
                       cell.backgroundColor = UIColor.white
                  }else{
                      cell.backgroundColor = UIColor.black
                  }
              } else{
                  if indexPath.row % 2 == 0 {
                      cell.backgroundColor = UIColor.black
                  }else{
                      cell.backgroundColor = UIColor.white
                  }
              }
          
              return cell
          }
    
    func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {
            // Divide the width by 3 to create a 3x3 grid
            let width = collectionView.frame.size.width / 4.0
            let height = width
            return CGSize(width: width, height: height)
        }
    
}

以下是CustomCollectionViewCell: UICollectionViewCell的型号:

class CustomCollectionViewCell: UICollectionViewCell {
   
    let titleLabel = UILabel()

    override init(frame: CGRect) {
        super.init(frame: frame)

        contentView.addSubview(titleLabel)

        titleLabel.translatesAutoresizingMaskIntoConstraints = false
        titleLabel.topAnchor.constraint(equalTo: contentView.topAnchor).isActive = true
        titleLabel.leadingAnchor.constraint(equalTo: contentView.leadingAnchor).isActive = true
        titleLabel.trailingAnchor.constraint(equalTo: contentView.trailingAnchor).isActive = true
        titleLabel.bottomAnchor.constraint(equalTo: contentView.bottomAnchor).isActive = true
    }

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

以及接收BoardViewController的实例的父视图

import UIKit

class MainViewController: UIViewController {

    let boardView = BoardViewController()
    override func viewDidLoad() {
        super.viewDidLoad()
        view.backgroundColor = .blue
        addBoardView()
    }
    
    func addBoardView(){
        addChild(boardView)
        view.addSubview(boardView.view)
        
     
        boardView.didMove(toParent: self)
    }
}

我试过在boardGamein topAnchorin constant: CGFloat的属性上做手脚.给出一些背景，这里是一个例子，我得到了boardGame.topAnchor.constraint(equalTo: view.topAnchor, constant: 20)，

如果我将CGFloat更改为200以使其更居中，则它内部CustomCollectionViewCell的属性将移动到边缘，影响上边距，如下所示:

我已经试图弄乱CustomCollectionViewCell内部的titleLabel个最上面的constraint个边距，但似乎什么都不做.

我如何才能在不影响CustomCollectionViewCell的边距的情况下将boardGame的视图保持在中心位置？