iOS UICollectionView：具有交替网格对齐的圆形视图的单元格

我正在尝试为圆形的自定义单元格实现

UICollectionView

。现在，默认情况下，这些圆的对齐方式与普通方形单元格相同：顶部圆和底部圆位于同一条垂直线上。如何将对齐方式更改为：顶部圆及其下方的两个圆形成一个等边三角形（顶部圆和底部圆的位置按半径长度移动）？详情如下:

from OOO
     OOO
     OOO

to   O O O
    O O O (no spacing among the circles)
     O O O

---

基本思想是创建一个自定义的

UICollectionViewLayout

，它实现：

• collectionViewContentSize

  ，即集合视图的完整、可滚动的

  contentSize

  的大小

• layouttributesforItem（在indexPath:）

  ，即特定单元格的关键属性（即

  中心

  和

  大小

  ）是什么；及

• layouttributesforements（在rect:）

  ，即，属于此特定

  rect

  的单元格的关键属性是什么。。。这将用于识别在任何给定时间点可见的单元格以及这些单元格的属性；这基本上是前一个方法中单元格的属性数组，过滤到该

  rect

  中的属性

因此，在Swift 3中，您可以执行以下操作：

class AlternatingGridLayout: UICollectionViewLayout {

    private var itemSize: CGSize!
    private var numberOfItems: Int!
    private var itemsPerRow: Int!
    private var rows: Int!
    private var circleViewCenterOffset: CGPoint!
    private var radiusOfCircleViews: CGFloat!
    private var insets: UIEdgeInsets!

    override func prepare() {
        super.prepare()

        guard let collectionView = collectionView else { return }

        radiusOfCircleViews = CGFloat(40.0)
        itemSize = CGSize(width: radiusOfCircleViews * 2, height: radiusOfCircleViews * 2)
        circleViewCenterOffset = CGPoint(x: 2 * radiusOfCircleViews * cos(.pi / 3),
                                         y: 2 * radiusOfCircleViews * sin(.pi / 3))
        numberOfItems = collectionView.numberOfItems(inSection: 0)
        itemsPerRow = Int(floor((collectionView.bounds.width - radiusOfCircleViews) / CGFloat(2 * radiusOfCircleViews)) + 0.5)
        rows = (numberOfItems - 1) / itemsPerRow + 1
        let excess = collectionView.bounds.width - (CGFloat(itemsPerRow) * radiusOfCircleViews * 2 + circleViewCenterOffset.x)
        insets = UIEdgeInsets(top: 10, left: excess / 2, bottom: 10, right: excess / 2)
    }

    override var collectionViewContentSize: CGSize {
        return CGSize(width: collectionView!.bounds.width,
                      height: 2 * radiusOfCircleViews + CGFloat(rows - 1) * circleViewCenterOffset.y + insets.top + insets.bottom)
    }

    override func layoutAttributesForItem(at indexPath: IndexPath) -> UICollectionViewLayoutAttributes? {
        let attributes = UICollectionViewLayoutAttributes(forCellWith: indexPath)

        attributes.center = centerForItem(at: indexPath)
        attributes.size = itemSize

        return attributes
    }

    override func layoutAttributesForElements(in rect: CGRect) -> [UICollectionViewLayoutAttributes]? {
        return (0 ..< collectionView!.numberOfItems(inSection: 0)).map { IndexPath(item: $0, section: 0) }
            .filter { rect.intersects(rectForItem(at: $0)) }
            .compactMap { self.layoutAttributesForItem(at: $0) }  // `flatMap` in Xcode versions before 9.3
    }

    private func centerForItem(at indexPath: IndexPath) -> CGPoint {
        let row = indexPath.item / itemsPerRow
        let col = indexPath.item - row * itemsPerRow

        var x: CGFloat = radiusOfCircleViews + CGFloat(col) * (radiusOfCircleViews * 2)
        let y: CGFloat = radiusOfCircleViews + CGFloat(row) * (circleViewCenterOffset.y)

        if row % 2 == 0 {
            x += circleViewCenterOffset.x
        }

        return CGPoint(x: x + insets.left, y: y + insets.top)
    }

    private func rectForItem(at indexPath: IndexPath) -> CGRect {
        let center = centerForItem(at: indexPath)

        return CGRect(x: center.x - radiusOfCircleViews, y: center.y - radiusOfCircleViews, width: radiusOfCircleViews * 2, height: radiusOfCircleViews * 2)
    }        
}

这将产生：

---

有关示例，请参见

---

---

注意，您提到希望“圆之间没有间距”，因此只需相应地调整

半径

和/或

项目大小

，即可获得所需的布局。

您需要创建自己的

UICollectionViewLayout

，“告诉”你的细胞的框架是什么。这很好，但你能告诉我如何让collectionview无限旋转，提前谢谢

class CircleLayout: UICollectionViewLayout {

    private var center: CGPoint!
    private var itemSize: CGSize!
    private var radius: CGFloat!
    private var numberOfItems: Int!

    override func prepare() {
        super.prepare()

        guard let collectionView = collectionView else { return }

        center = CGPoint(x: collectionView.bounds.midX, y: collectionView.bounds.midY)
        let shortestAxisLength = min(collectionView.bounds.width, collectionView.bounds.height)
        itemSize = CGSize(width: shortestAxisLength * 0.1, height: shortestAxisLength * 0.1)
        radius = shortestAxisLength * 0.4
        numberOfItems = collectionView.numberOfItems(inSection: 0)
    }

    override var collectionViewContentSize: CGSize {
        return collectionView!.bounds.size
    }

    override func layoutAttributesForItem(at indexPath: IndexPath) -> UICollectionViewLayoutAttributes? {
        let attributes = UICollectionViewLayoutAttributes(forCellWith: indexPath)

        let angle = 2 * .pi * CGFloat(indexPath.item) / CGFloat(numberOfItems)

        attributes.center = CGPoint(x: center.x + radius * cos(angle), y: center.y + radius * sin(angle))
        attributes.size = itemSize

        return attributes
    }

    override func layoutAttributesForElements(in rect: CGRect) -> [UICollectionViewLayoutAttributes]? {
        return (0 ..< collectionView!.numberOfItems(inSection: 0))
            .compactMap { item -> UICollectionViewLayoutAttributes? in    // `flatMap` in Xcode versions prior to 9.3
                self.layoutAttributesForItem(at: IndexPath(item: item, section: 0))
        }
    }
}

class ViewController: UICollectionViewController {

    var numberOfCells = 10

    override func viewDidLoad() {
        super.viewDidLoad()

        collectionView?.collectionViewLayout = CircleLayout()

        // just for giggles and grins, let's show the insertion of a cell

        DispatchQueue.main.asyncAfter(deadline: .now() + 2) {
            self.collectionView?.performBatchUpdates({
                self.numberOfCells += 1
                self.collectionView?.insertItems(at: [IndexPath(item: 0, section: 0)])
            }, completion: nil)
        }
    }

}

// MARK: UICollectionViewDataSource

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

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