Merge pull request #14 from VladIacobIonut/ShazamEffect

Shazam card stack effect implementation

Sources/VerticalCardSwiperFlowLayout.swift

@@ -40,13 +40,14 @@ internal class VerticalCardSwiperFlowLayout: UICollectionViewFlowLayout {
     }
 
     internal override func layoutAttributesForElements(in rect: CGRect) -> [UICollectionViewLayoutAttributes]? {
-        let items = NSArray (array: super.layoutAttributesForElements(in: rect)!, copyItems: true)
+        let items = NSMutableArray (array: super.layoutAttributesForElements(in: rect)!, copyItems: true)
 
         items.enumerateObjects(using: { (object, index, stop) -> Void in
             let attributes = object as! UICollectionViewLayoutAttributes
 
             self.updateCellAttributes(attributes)
         })
+
         return items as? [UICollectionViewLayoutAttributes]
     }
 
@@ -66,32 +67,32 @@ internal class VerticalCardSwiperFlowLayout: UICollectionViewFlowLayout {
 
         // Page height used for estimating and calculating paging.
         let pageHeight = cellHeight + self.minimumLineSpacing
-
+        
         // Make an estimation of the current page position.
         let approximatePage = self.collectionView!.contentOffset.y/pageHeight
 
         // Determine the current page based on velocity.
         let currentPage = (velocity.y < 0.0) ? floor(approximatePage) : ceil(approximatePage)
 
         // Create custom flickVelocity.
-        let flickVelocity = velocity.y * 0.3
+        let flickVelocity = velocity.y * 0.4
 
         // Check how many pages the user flicked, if <= 1 then flickedPages should return 0.
         let flickedPages = (abs(round(flickVelocity)) <= 1) ? 0 : round(flickVelocity)
 
         // Calculate newVerticalOffset.
         let newVerticalOffset = ((currentPage + flickedPages) * pageHeight) - self.collectionView!.contentInset.top
-
+        
         return CGPoint(x: proposedContentOffset.x, y: newVerticalOffset)
     }
 
     internal override func finalLayoutAttributesForDisappearingItem(at itemIndexPath: IndexPath) -> UICollectionViewLayoutAttributes? {
-
+        
         // make sure the zIndex of the next card is higher than the one we're swiping away.
         let nextIndexPath = IndexPath(row: itemIndexPath.row + 1, section: itemIndexPath.section)
         let nextAttr = self.layoutAttributesForItem(at: nextIndexPath)
         nextAttr?.zIndex = nextIndexPath.row
-
+        
         // attributes for swiping card away
         let attr = self.layoutAttributesForItem(at: itemIndexPath)
 
@@ -104,18 +105,30 @@ internal class VerticalCardSwiperFlowLayout: UICollectionViewFlowLayout {
      - parameter attributes: The attributes we're updating.
      */
     fileprivate func updateCellAttributes(_ attributes: UICollectionViewLayoutAttributes) {
-        let minY = collectionView!.bounds.minY + collectionView!.contentInset.top
+
+        var minY = collectionView!.bounds.minY + collectionView!.contentInset.top
         let maxY = attributes.frame.origin.y
 
+        if minY > attributes.frame.origin.y + attributes.bounds.height + minimumLineSpacing + collectionView!.contentInset.top {
+            minY = 0
+        }
+
         let finalY = max(minY, maxY)
         var origin = attributes.frame.origin
         let deltaY = (finalY - origin.y) / attributes.frame.height
+        let translationScale = CGFloat((attributes.zIndex + 1) * 10)
 
+        // Card stack effect
         if let itemTransform = firstItemTransform {
             let scale = 1 - deltaY * itemTransform
-            attributes.transform = CGAffineTransform(scaleX: scale, y: scale)
-            // TODO: add card stack effect (like Shazam)
+            var t = CGAffineTransform.identity
+            t = t.scaledBy(x: scale, y: 1)
+            t = t.translatedBy(x: 0, y: (deltaY * translationScale))
+
+            attributes.transform = t
         }
+
+        origin.x = (self.collectionView?.frame.width)! / 2 - attributes.frame.width / 2 - (self.collectionView?.contentInset.left)!
         origin.y = finalY
         attributes.frame = CGRect(origin: origin, size: attributes.frame.size)
         attributes.zIndex = attributes.indexPath.row