iOS UICollectionView：在交替网格对齐中具有圆形视图的单元格

Question

我正在尝试为圆形的自定义单元格实施 UICollectionView。现在默认情况下，圆圈的对齐方式与普通方形单元格相同：顶部圆圈和底部圆圈位于同一垂直线上。我怎样才能改变对齐方式：顶部圆和它下面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）？如下：

from OOO
     OOO
     OOO

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

Answer 1

基本思路是创建自定义 UICollectionViewLayout 实现：

collectionViewContentSize，即集合视图的完整可滚动 contentSize 的大小是多少；
layoutAttributesForItem(at indexPath:)，即特定单元格的关键属性（即center和size）是什么；和
layoutAttributesForElements(in rect:)，即属于此特定 rect 的单元格的关键属性是什么......这将用于识别哪些单元格在任何时候都可见给定时间点以及这些单元格的属性；这基本上是先前方法中单元格属性的数组，过滤到 rect 中的单元格。

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: [=10=], section: 0) }
            .filter { rect.intersects(rectForItem(at: [=10=])) }
            .compactMap { self.layoutAttributesForItem(at: [=10=]) }  // `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)
    }        
}

产量：

很明显，您可以根据需要自定义它，但它说明了基本思想。

在下面我的原始回答中，我假设您希望在一个圆圈中看到这些单元格，如 WWDC 2012 视频 Advanced Collection Views and Building Custom Layouts 中所示（视频大约 40 多分钟）。见下文。

例如，在Swift 3:

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))
        }
    }
}

然后您可以简单地设置 collectionViewLayout 然后执行标准 UICollectionViewDataSource 方法。

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
    }
}

产量：

参见 https://github.com/robertmryan/CircularCollectionView 示例。

注意，你提到你想要 "no spacing among the circles"，所以只需相应地调整 radius and/or itemSize 以获得你想要的布局。

iOS UICollectionView：在交替网格对齐中具有圆形视图的单元格

iOS UICollectionView: Cells with circular view in alternating grid alignment

ios

uicollectionview

uicollectionviewlayout