Get cell index cell in center of view collection in swift?

Question

I tried this to get the index of the cell at the center of the collection view using the uicollectionview extension, but I always get zero instead of index. How can i fix this?

extension UICollectionView { var centerPoint : CGPoint { get { return CGPoint(x: self.center.x + self.contentOffset.x, y: self.center.y + self.contentOffset.y); } } var centerCellIndexPath: NSIndexPath? { if let centerIndexPath: NSIndexPath = self.indexPathForItemAtPoint(self.centerPoint) { return centerIndexPath } return nil } } 

then: in a UIViewController in a random method, I have this:

 if let centerCellIndexPath: NSIndexPath = collectionTemp!.centerCellIndexPath { print(centerCellIndexPath) } else { println("nil") } 

the index path is always zero, and I don’t understand why, because the cells are displayed in order, everything is fine except for this.

Answer 1

I managed to solve my problem using a special layout that always keeps the cell in the center. Using this, the indexPath in the center can never be nil.

  class CenterFlowLayout: UICollectionViewFlowLayout { override func targetContentOffsetForProposedContentOffset(proposedContentOffset: CGPoint, withScrollingVelocity velocity: CGPoint) -> CGPoint { if let cv = self.collectionView { let cvBounds = cv.bounds let halfWidth = cvBounds.size.width * 0.5 let proposedContentOffsetCenterX = proposedContentOffset.x + halfWidth if let attributesForVisibleCells = self.layoutAttributesForElementsInRect(cvBounds) as [UICollectionViewLayoutAttributes]! { var candidateAttributes: UICollectionViewLayoutAttributes? for attributes in attributesForVisibleCells { // == Skip comparison with non-cell items (headers and footers) == // if attributes.representedElementCategory != UICollectionElementCategory.Cell { continue } if let candAttrs = candidateAttributes { let a = attributes.center.x - proposedContentOffsetCenterX let b = candAttrs.center.x - proposedContentOffsetCenterX if fabsf(Float(a)) < fabsf(Float(b)) { candidateAttributes = attributes } } else { // == First time in the loop == // candidateAttributes = attributes continue } } return CGPoint(x : candidateAttributes!.center.x - halfWidth, y : proposedContentOffset.y) } } // Fallback return super.targetContentOffsetForProposedContentOffset(proposedContentOffset) } } 

Add this as a subclass of UICollectionFlowLayout.