如何在 swift 的 collectionview 上显示重叠的标题？

Question

我正在尝试构建像 iPhone 这样的照片库，但我在使用 CollectionView 时遇到了问题。 标题没有显示出来，我不知道为什么。

 override func viewDidLoad() {
    super.viewDidLoad()
    
    
    layout.itemSize = CGSize(width: view.frame.width/3, height: view.frame.width/3)
    
    collectionView = UICollectionView(frame: .zero, collectionViewLayout: layout)
    collectionView.translatesAutoresizingMaskIntoConstraints = false
    collectionView.backgroundColor = .white
    collectionView.register(ImageCell.self, forCellWithReuseIdentifier: "ImageCell")
    collectionView.dataSource = self
    collectionView.delegate = self
    
    view.addSubview(titleView)
    view.addSubview(collectionView)
    view.addSubview(button)
    
    NSLayoutConstraint.activate([
        titleView.topAnchor.constraint(equalTo: view.safeAreaLayoutGuide.topAnchor, constant: 16),
        titleView.leadingAnchor.constraint(equalTo: view.safeAreaLayoutGuide.leadingAnchor,constant: 16),
        titleView.trailingAnchor.constraint(equalTo: view.safeAreaLayoutGuide.trailingAnchor,constant: 16),
        titleView.bottomAnchor.constraint(equalTo: collectionView.topAnchor, constant: -16),
        
        collectionView.topAnchor.constraint(equalTo: titleView.bottomAnchor, constant: 200),
        collectionView.leadingAnchor.constraint(equalTo: view.safeAreaLayoutGuide.leadingAnchor),
        collectionView.trailingAnchor.constraint(equalTo: view.safeAreaLayoutGuide.trailingAnchor),
        collectionView.bottomAnchor.constraint(equalTo: view.bottomAnchor),
        
        button.bottomAnchor.constraint(equalTo: view.safeAreaLayoutGuide.bottomAnchor, constant: -8),
        button.rightAnchor.constraint(equalTo: view.rightAnchor, constant: -8),
        button.widthAnchor.constraint(equalToConstant: 50),
        button.heightAnchor.constraint(equalToConstant: 50)
    ])
}

Answer 1

您的约束是相互冲突的。

第一：为 TitleView 设置高度。

第二：在标题视图和集合视图之间只设置一个绑定。 你用不同的选项设置了两次。

 NSLayoutConstraint.activate([
    titleView.topAnchor.constraint(
       equalTo: view.safeAreaLayoutGuide.topAnchor, constant: 16
    ),
    titleView.leadingAnchor.constraint(
       equalTo: view.safeAreaLayoutGuide.leadingAnchor,constant: 16
    ),
    titleView.trailingAnchor.constraint(
      equalTo: view.safeAreaLayoutGuide.trailingAnchor,constant: -16
    ),
    titleView.heightAnchor.constraint(
       equalToConstant: 80
    ),
    
    collectionView.topAnchor.constraint(
      equalTo: titleView.bottomAnchor
    ),
    collectionView.leadingAnchor.constraint(
      equalTo: view.safeAreaLayoutGuide.leadingAnchor
    ),
    collectionView.trailingAnchor.constraint(
      equalTo: view.safeAreaLayoutGuide.trailingAnchor
    ),
    collectionView.bottomAnchor.constraint(
      equalTo: view.bottomAnchor
    ),
    
    button.bottomAnchor.constraint(
      equalTo: view.safeAreaLayoutGuide.bottomAnchor, constant: -8
    ),
    button.rightAnchor.constraint(
      equalTo: view.rightAnchor, constant: -8
    ),
    button.widthAnchor.constraint(
      equalToConstant: 50
    ),
    button.heightAnchor.constraint(
      equalToConstant: 50
    )
  ])