custom collection view layout that allows you to page by cell, not screen

use cocoapods to install PagingCollectionViewLayout by adding it to your Podfile:

platform :ios, '9.0'
use_frameworks!
pod 'PagingCollectionViewLayout'

import PagingCollectionViewLayout

add PagingCollectionViewLayout.swift to your project

instantiate a layout property

let layout = PagingCollectionViewLayout()

set the following properties

layout.itemSize = 
layout.minimumLineSpacing = 
layout.scrollDirection = .horizontal

instantiate a collection view using the layout property

let collectionView = UICollectionView(frame: .zero, collectionViewLayout: layout)

for snappy scrolling set the following

collectionView.decelerationRate = .fast

collectionView.isPagingEnabled = true

layout.scrollDirection = .vertical

or since the default is vertical

layout.scrollDirection = .horizontal

• center the item in focus
• allow the previous item to be visible

set the following property

layout.sectionInset = 

• horizontal collection view - set left and right insets
• vertical collection view - set top and bottom insets

layout.velocityThresholdPerPage determines the velocity needed to skip an item (default = 2.0)

• a non zero swipe velocity will result in the collection view scrolling to the prev/next item
• the number of items skipped = swipe velocity / velocityThresholdPerPage

layout.numberOfItemsPerPage = 2