Steven.B Steven.B - 2 months ago 16
Swift Question

Circular UICollectionview, how to all keep cell's angles 0°

I build a circular UICollectionview by following This guide, Everything is working as expected but I don't want the items to rotate around their own angle/anchor

The top row is how my circular collectionview is working at the moment, the bottom drawing is how I would like my collectionview :

Design

I am using following layout attribute code:

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
}
}


with the following layout class:

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
}
}


I tried many things but I was not able to change the cell rotation

Answer

I've solved this problem by rotateing the view of cell by negative angle:

Code below:

      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)
}
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