title: UICollectionViewLayout methods never get called
body: <p>I am working with a <code>UICollectionView</code> and I am trying to use the <code>UICollectionViewLayout</code> methods to adjust the sizing of the cell however they are never being called. The methods are :</p>
  
  <p><code>sizeForItemAtIndexPath</code>, <code>minimumInterimItemSpacingForSectionAtIndex</code>, and <code>minimumLineSpacingForSectionAtIndex</code> </p>
  
  <p>these 3 methods are never being called and I'm not sure where/ how to call them from. below is my code in Swift 3</p>
  
  <pre><code>import Foundation
  import UIKit
  
  class CollectionVC: UICollectionViewController {
  
      var Sections = [SectionService]()
  
      override func viewDidLoad() {
          createServiceSections()
      }
  
      func createServiceSections(){
  
          ServiceSections.append(ServiceSection(headerTitle: "1", items: 2, headerImage: UIImage(named: "Default"), stats: nil))
          ServiceSections.append(ServiceSection(headerTitle: "2", items: 3, headerImage: UIImage(named: "Default"), stats: nil))
          ServiceSections.append(ServiceSection(headerTitle: "3", items: 3, headerImage: UIImage(named: "Default"), stats: nil))
          ServiceSections.append(ServiceSection(headerTitle: "4", items: 5, headerImage: UIImage(named: "Default"), stats: nil))
      }
  
      override func numberOfSections(in collectionView: UICollectionView) -&gt; Int {
          return ServiceSections.count
      }
  
  
      override func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -&gt; Int {
          return ServiceSections[indexPath.section].items.count
      }
  
      override func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -&gt; UICollectionViewCell {
  
          let cell1 = collectionView.dequeueReusableCell(withReuseIdentifier: "servicecell", for: indexPath) as! ServicesCellView
  
          cell1.serviceLabel.text = "test"
          cell1.serviceImage.image = ServiceSections[indexPath.section].headerImage
          return cell1
      }
  
      func collectionView(collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAtIndexPath indexPath: NSIndexPath) -&gt; CGSize {
  
          print("size for item at indexPath")
          var cellSize: CGSize
          let collectionViewWidth = self.collectionView!.bounds.size.width
          cellSize = CGSize(width: (collectionViewWidth * 0.48), height: (collectionViewWidth * 0.48))
          return cellSize
      }
  
      func collectionView(collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, minimumInterItemSpacingForSectionAtIndex section: Int) -&gt; CGFloat {
          print("min spacing section")
          return 1
      }
  
      func collectionView(collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, minimumLineSpacingForSectionAtIndex section: Int) -&gt; CGFloat {
          print("min line spacing section")
          return 1
      }
  }
  </code></pre>