title: UICollectionView didSelectItemAt not being called
body: <p>I am puzzled because It is just a simple thing but doesn't work.</p>
  
  <p>This is my checked list before write question at here.</p>
  
  <ol>
  <li><p>UICollectionViewDelegate is registered</p></li>
  <li><p>There is nothing on above than UICollectionView from "Debug View Hierarchy"</p></li>
  <li><p><code>isUserInteractionEnabled</code> of UICollectionView and UICollectionViewCell is <code>true</code></p></li>
  <li><p><code>isAllowsSelection</code> of UICollectionView is <code>true</code></p></li>
  </ol>
  
  <p>Is there anything else I should check out?</p>
  
  <p>=====</p>
  
  <pre><code>class MyView: NibDesignable { // It's UIView with NibDesignableProtocol (https://github.com/mbogh/NibDesignable)
      @IBOutlet weak var collectionView: UICollectionView!
  
      override init(frame: CGRect) {
          super.init(frame: frame)
  
          self.setup()
      }
  
      required init?(coder aDecoder: NSCoder) {
          super.init(coder: aDecoder)
  
          self.setup()
      }
  
      private func setup() {
          print("test - It's called.")
  
          self.collectionView.dataSource = self
          self.collectionView.delegate = self
          self.collectionView.isUserInteractionEnabled = true
          self.collectionView.isAllowsSelection = true
      }
  }
  
  extension MyView: UICollectionViewDataSource, UICollectionViewDelegate, UICollectionViewDelegateFlowLayout {
      func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath {
          print("test - It's not called")
      }
  }
  </code></pre>
  
  <p>I pasted only the part relating to question because all of code is too long.</p>