圆形UICollectionview，如何保持所有单元格角度为0°

Posted 2021-04-21

我按照This指南建立了一个圆形UICollectionview，一切都按预期工作但我不希望这些项目围绕他们自己的角度/锚点旋转

第一行是我的圆形collectionview当前是如何工作的，底部绘图是我想要我的collectionview的方式：

我使用以下布局属性代码：

class CircularCollectionViewLayoutAttributes: UICollectionViewLayoutAttributes {

var anchorPoint = CGPoint(x: 0.3, y: 0.5)

var angle: CGFloat = 0 {
    didSet {
        zIndex = Int(angle*1000000)
        transform = CGAffineTransformMakeRotation(angle)
    }
}

override func copyWithZone(zone: NSZone) -> AnyObject {
    let copiedAttributes: CircularCollectionViewLayoutAttributes = super.copyWithZone(zone) as! CircularCollectionViewLayoutAttributes
    copiedAttributes.anchorPoint = self.anchorPoint
    copiedAttributes.angle = self.angle
    return copiedAttributes
}
}

使用以下布局类：

class CircularCollectionViewLayout: UICollectionViewLayout {
let itemSize = CGSize(width: 60, height: 110)
var angleAtExtreme: CGFloat {

    return collectionView!.numberOfItemsInSection(0) > 0 ? -CGFloat(collectionView!.numberOfItemsInSection(0)-1)*anglePerItem : 0
}

var angle: CGFloat {
    return angleAtExtreme*collectionView!.contentOffset.x/(collectionViewContentSize().width - CGRectGetWidth(collectionView!.bounds))
}

var radius: CGFloat = 400 {
    didSet {
        invalidateLayout()
    }
}

var anglePerItem: CGFloat {
    return 0.18
}

var attributesList = [CircularCollectionViewLayoutAttributes]()

override func collectionViewContentSize() -> CGSize {
    return CGSize(width: CGFloat(collectionView!.numberOfItemsInSection(0))*itemSize.width,
                  height: CGRectGetHeight(collectionView!.bounds))
}

override class func layoutAttributesClass() -> AnyClass {
    return CircularCollectionViewLayoutAttributes.self
}

override func prepareLayout() {
    super.prepareLayout()
    let centerX = collectionView!.contentOffset.x + (CGRectGetWidth(collectionView!.bounds)/2.0)
    let anchorPointY = ((itemSize.height/2.0) + radius)/itemSize.height

    let theta = atan2(CGRectGetWidth(collectionView!.bounds)/2.0, radius + (itemSize.height/2.0) - (CGRectGetHeight(collectionView!.bounds)/2.0)) //1
    //let theta:CGFloat = 1.0


    var startIndex = 0
    var endIndex = collectionView!.numberOfItemsInSection(0) - 1

    if (angle < -theta) {
        startIndex = Int(floor((-theta - angle)/anglePerItem))
    }

    endIndex = min(endIndex, Int(ceil((theta - angle)/anglePerItem)))

    if (endIndex < startIndex) {
        endIndex = 0
        startIndex = 0
    }
    attributesList = (startIndex...endIndex).map { (i) -> CircularCollectionViewLayoutAttributes in
        let attributes = CircularCollectionViewLayoutAttributes(forCellWithIndexPath: NSIndexPath(forItem: i, inSection: 0))
        attributes.size = self.itemSize
        attributes.center = CGPoint(x: centerX, y: CGRectGetMidY(self.collectionView!.bounds))
        attributes.angle = self.angle + (self.anglePerItem*CGFloat(i))
        attributes.anchorPoint = CGPoint(x: 0.5, y: anchorPointY)
        return attributes
    }
}

override func layoutAttributesForElementsInRect(rect: CGRect) -> [UICollectionViewLayoutAttributes]? {
    return attributesList
}

override func layoutAttributesForItemAtIndexPath(indexPath: NSIndexPath)
    -> (UICollectionViewLayoutAttributes!) {
        return attributesList[indexPath.row]
}

override func shouldInvalidateLayoutForBoundsChange(newBounds: CGRect) -> Bool {
    return true
}


override func targetContentOffsetForProposedContentOffset(proposedContentOffset: CGPoint, withScrollingVelocity velocity: CGPoint) -> CGPoint {
    var finalContentOffset = proposedContentOffset
    let factor = -angleAtExtreme/(collectionViewContentSize().width - CGRectGetWidth(collectionView!.bounds))
    let proposedAngle = proposedContentOffset.x*factor
    let ratio = proposedAngle/anglePerItem
    var multiplier: CGFloat
    if (velocity.x > 0) {
        multiplier = ceil(ratio)
    } else if (velocity.x < 0) {
        multiplier = floor(ratio)
    } else {
        multiplier = round(ratio)
    }
    finalContentOffset.x = multiplier*anglePerItem/factor
    return finalContentOffset
}
}

我尝试了很多东西但是我无法改变细胞旋转

答案

我通过负角度旋转单元格来解决这个问题：

代码如下：

      override func applyLayoutAttributes(layoutAttributes: UICollectionViewLayoutAttributes!) {
super.applyLayoutAttributes(layoutAttributes)
let circularlayoutAttributes = layoutAttributes as! CircularCollectionViewLayoutAttributes
self.layer.anchorPoint = circularlayoutAttributes.anchorPoint

viewRoot.transform = CGAffineTransformMakeRotation(-circularlayoutAttributes.angle)

self.center.y += (circularlayoutAttributes.anchorPoint.y - 0.5) * CGRectGetHeight(self.bounds)
}