我想通过修改约束属性(例如
boardGame: UICollectionView
)将 UIView topAnchor
的位置移动到屏幕的中心,但我对其所做的任何操作似乎都会影响其中的内容。我还定义了一个 UICollectionViewCell
模型,这样我就可以将 boardGame
中的单元格注册为“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)
}
}
这是
CustomCollectionViewCell: UICollectionViewCell
模型:
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
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)
}
}
我尝试过使用
constant: CGFloat
中 topAnchor
中 boardGame
的属性。这里提供一些背景信息,这是我通过 boardGame.topAnchor.constraint(equalTo: view.topAnchor, constant: 20)
, 得到的示例
如果我将
CGFloat
更改为 200 以使其更加居中,则其内部 CustomCollectionViewCell
的属性会移动到影响上边距的边缘,如下所示:
我已经尝试弄乱
titleLabel
顶部边距constraint
内部CustomCollectionViewCell
但似乎没有做任何事情。
如何才能使
boardGame
视图保持在中心而不影响CustomCollectionViewCell
的边缘?
单元格位于集合视图的顶部边缘,因为这就是集合视图的工作方式。这是设计使然。当集合视图位于屏幕顶部时,单元格仅出现“居中”,因为默认情况下单元格的布局是为了避开安全区域(在本例中为动态岛)。
无论如何,你的约束都是矛盾的。你是说
boardGame
视图应该有固定的宽度和高度(假设父视图的宽度和高度是固定的),并且它的中心点应该与父视图的中心点相同(centerX = view.centerX
和centerY = view.centerY
), 并且它的顶部距离超级视图的顶部仅20点。
这些不可能同时满足。正如您在第一个屏幕截图中看到的,
centerY = view.centerY
约束被打破,以满足其他约束。
如果您希望集合视图垂直和水平居中,只需删除顶部边距约束:
boardGame.topAnchor.constraint(equalTo: view.topAnchor, constant: margin)
如果还希望单元格垂直居中,可以设置
contentOffset
:
override func viewDidAppear(_ animated: Bool) {
super.viewDidAppear(animated)
boardGame.contentOffset.y = (boardGame.contentSize.height - boardGame.bounds.height) / 2
}
也就是说,如果
boardGame
不应该是可滚动的,请考虑为此布局使用一系列 UIStackView
。