UICollectionView horizontal paging with 3 items

Question

I need to show 3 items in a UICollectionView, with paging enabled like this

Answer 1

Swift 3.0 Complete Solution based on Raheel Sadiq

var isfirstTimeTransform:Bool = true

func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {


    let cell : UICollectionViewCell = collectionView.dequeueReusableCell(withReuseIdentifier: "YourCustomViewCell", for: indexPath)

    if (indexPath.row == 0 && isfirstTimeTransform) { 
        isfirstTimeTransform = false
    }else{
        cell.transform = CGAffineTransform(scaleX: 0.8, y: 0.8) 
    }

    return cell
}

func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {

    return CGSize(width: collectionView.bounds.width/3, height: collectionView.bounds.height)
}

func scrollViewWillEndDragging(_ scrollView: UIScrollView, withVelocity velocity: CGPoint, targetContentOffset: UnsafeMutablePointer) {
    // Simulate "Page" Function
    let pageWidth: Float = Float(self.collectionView.frame.width/3 + 20)
    let currentOffset: Float = Float(scrollView.contentOffset.x)
    let targetOffset: Float = Float(targetContentOffset.pointee.x)
    var newTargetOffset: Float = 0
    if targetOffset > currentOffset {
        newTargetOffset = ceilf(currentOffset / pageWidth) * pageWidth
    }
    else {
        newTargetOffset = floorf(currentOffset / pageWidth) * pageWidth
    }
    if newTargetOffset < 0 {
        newTargetOffset = 0
    }
    else if (newTargetOffset > Float(scrollView.contentSize.width)){
        newTargetOffset = Float(Float(scrollView.contentSize.width))
    }

    targetContentOffset.pointee.x = CGFloat(currentOffset)
    scrollView.setContentOffset(CGPoint(x: CGFloat(newTargetOffset), y: scrollView.contentOffset.y), animated: true)

    // Make Transition Effects for cells
    let duration = 0.2
    var index = newTargetOffset / pageWidth;
    var cell:UICollectionViewCell = self.collectionView.cellForItem(at: IndexPath(row: Int(index), section: 0))!
    if (index == 0) { // If first index
        UIView.animate(withDuration: duration, delay: 0.0, options: [ .curveEaseOut], animations: {
            cell.transform = CGAffineTransform.identity
        }, completion: nil)
        index += 1
        cell = self.collectionView.cellForItem(at: IndexPath(row: Int(index), section: 0))!
        UIView.animate(withDuration: duration, delay: 0.0, options: [ .curveEaseOut], animations: {
            cell.transform = CGAffineTransform(scaleX: 0.8, y: 0.8)
        }, completion: nil)
    }else{
        UIView.animate(withDuration: duration, delay: 0.0, options: [ .curveEaseOut], animations: {
            cell.transform = CGAffineTransform.identity;
        }, completion: nil)

        index -= 1 // left
        if let cell = self.collectionView.cellForItem(at: IndexPath(row: Int(index), section: 0)) {
            UIView.animate(withDuration: duration, delay: 0.0, options: [ .curveEaseOut], animations: {
                cell.transform = CGAffineTransform(scaleX: 0.8, y: 0.8);
            }, completion: nil)
        }

        index += 1
        index += 1 // right
        if let cell = self.collectionView.cellForItem(at: IndexPath(row: Int(index), section: 0)) {
            UIView.animate(withDuration: duration, delay: 0.0, options: [ .curveEaseOut], animations: {
                cell.transform = CGAffineTransform(scaleX: 0.8, y: 0.8);
            }, completion: nil)
        }
    }

}