title: UICollectionView error: cells must be retrieved by calling -: -dequeueReusableCellWithReuseIdentifier:forIndexPath:
body: <p>In my project I have multiple types of <code>UITableview</code> cell each containing <code>UICollectionview</code>. </p>
  
  <p>Initially I loaded 2 <code>tableViewcell</code> in 2 sections of <code>UITableview</code>. At first it loads fine without any problem. If I scroll the first section it scrolls nice but when I try to scroll the second section it gives me the following error: </p>
  
  <blockquote>
    <p>the cell returned from -collectionView:cellForItemAtIndexPath: does not have a reuseIdentifier - cells must be retrieved by calling -dequeueReusableCellWithReuseIdentifier:forIndexPath:</p>
  </blockquote>
  
  <p>I have the following code to set up the process:</p>
  
  <pre><code>    class Home: UITableViewDelegate, UITableViewDataSource, UICollectionViewDelegate, UICollectionViewDataSource{
  
       override func viewDidLoad() {
          self.tableView.register(SliderViewCell.nib, forCellReuseIdentifier: SliderViewCell.identifier)
          self.tableView.register(GridViewCell.nib, forCellReuseIdentifier: GridViewCell.identifier)
          self.tableView.estimatedRowHeight = 80
          self.tableView.rowHeight = UITableViewAutomaticDimension
  
  }
  func numberOfSections(in tableView: UITableView) -&gt; Int {
      return 2
  }
  func tableView(_ tableView: UITableView, willDisplay cell: UITableViewCell, forRowAt indexPath: IndexPath) {
  
      let viewObj = self.viewObject[indexPath.section]
      if viewObj.itemType! == HomeViewItemType.Slider.rawValue{
      if let sliderCell = cell as? SliderViewCell {
          sliderCell.setCollectionViewDataSourceDelegate(self, forRow: indexPath.row)
      }
      }
      else if viewObj.itemType! == HomeViewItemType.Grid.rawValue{
      if let gridCell = cell as? GridViewCell {
          gridCell.setCollectionViewDataSourceDelegate(self, forRow: indexPath.row)
      }
      }
  
  
  }
  func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -&gt; Int {
      return 1
  }
  func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -&gt; UITableViewCell {
      if self.viewObject.count&gt;0{
      let viewObj = self.viewObject[indexPath.section]
      if viewObj.itemType! == HomeViewItemType.Slider.rawValue{
          let cell:SliderViewCell = tableView.dequeueReusableCell(withIdentifier: SliderViewCell.identifier, for: indexPath) as! SliderViewCell
          cell.contentView.tag = indexPath.section
      return cell
  }
  else if viewObj.itemType! == HomeViewItemType.Grid.rawValue{
          let cell:GridViewCell = tableView.dequeueReusableCell(withIdentifier: GridViewCell.identifier, for: indexPath) as! GridViewCell
          cell.contentView.tag = indexPath.section
          return cell
  }
      }
      return UITableViewCell()
  }
  func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {
      print("selected")
  }
  
  func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -&gt; Int {
  
          return self.viewObject[section].viewData.count
  
  }
  
  func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -&gt; UICollectionViewCell {
  
      if viewObj.itemType! == HomeViewItemType.Slider.rawValue{
          if let cell:SliderCollectionViewCell = collectionView.dequeueReusableCell(withReuseIdentifier: SliderCollectionViewCell.identifier, for: indexPath) as? SliderCollectionViewCell{
  
              if viewObj.viewData.count&gt;0{
                  if let imageURL = URL(string: viewData.imageLink!){
                      cell.icon.sd_setImage(with: imageURL, completed: nil)
                  }
              }
              return cell
          }
      }
      else if viewObj.itemType! == HomeViewItemType.Grid.rawValue{
  if let cell:GridCollectionViewCell = collectionView.dequeueReusableCell(withReuseIdentifier: GridCollectionViewCell.identifier, for: indexPath) as? GridCollectionViewCell{
  
              if viewObj.viewData.count&gt;0{
                  if let imageURL = URL(string: viewData.icon!){
                      cell.icon.sd_setImage(with: imageURL, completed: nil)
                  }
  
              }
  
              return cell
  }
      }
  
      return UICollectionViewCell()
  }
  
  func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
      print("tapped")
  }
  
      }
  
  class SliderViewCell: UITableViewCell {
  
  @IBOutlet weak var collectionView: UICollectionView!
  static var nib:UINib {
      return UINib(nibName: identifier, bundle: nil)
  }
  static var identifier:String {
      return String(describing: SliderViewCell.self)
  }
  var collectionViewCellWidth : CGFloat = 15.0
  var collectionViewCellHeight : CGFloat = 150.0
  var cellSpaceWidth : CGFloat = 8.0
  
  override func awakeFromNib() {
      super.awakeFromNib()
      self.configureCollectionViewCell(nibFile: SliderCollectionViewCell.nib, identifier: SliderCollectionViewCell.identifier, width: collectionView.frame.size.width, height: 80, topInset: 0, leftInset: 0, bottomInset: 0, rightInset: 0, cellSpace: cellSpaceWidth, interimSpace: 0.0, scrollInDirection: .horizontal)
  }
  
  override func setSelected(_ selected: Bool, animated: Bool) {
      super.setSelected(selected, animated: animated)
  
      // Configure the view for the selected state
  }
  }
  class GridViewCell: UITableViewCell {
  
  @IBOutlet weak var collectionView: UICollectionView!
  static var nib:UINib {
      return UINib(nibName: identifier, bundle: nil)
  }
  static var identifier:String {
      return String(describing: GridViewCell.self)
  }
  var collectionViewCellWidth : CGFloat = 15.0
  var collectionViewCellHeight : CGFloat = 150.0
  var cellSpaceWidth : CGFloat = 8.0
  
  override func awakeFromNib() {
      super.awakeFromNib()
      self.configureCollectionViewCell(nibFile: GridCollectionViewCell.nib, identifier: GridCollectionViewCell.identifier, width: collectionView.frame.size.width, height: 80, topInset: 0, leftInset: 0, bottomInset: 0, rightInset: 0, cellSpace: cellSpaceWidth, interimSpace: 0.0, scrollInDirection: .horizontal)
  }
  
  func configureCollectionViewCell(nibFile:UINib, identifier:String,width:CGFloat,height:CGFloat, topInset:CGFloat,leftInset:CGFloat,bottomInset:CGFloat,rightInset:CGFloat, cellSpace:CGFloat, interimSpace:CGFloat,scrollInDirection:UICollectionViewScrollDirection){
  
      let nib = nibFile
      collectionView.register(nib, forCellWithReuseIdentifier: identifier)
      let cellWidth : CGFloat = width//collectionView.frame.size.width
      let cellheight : CGFloat = height//collectionViewCellHeight
      let cellSize = CGSize(width: cellWidth , height:cellheight)
      let layout = UICollectionViewFlowLayout()
      layout.scrollDirection = scrollInDirection
      layout.itemSize = cellSize
      layout.sectionInset = UIEdgeInsets(top: topInset, left: leftInset, bottom: bottomInset, right: rightInset)
      layout.minimumLineSpacing = cellSpace
      layout.minimumInteritemSpacing = interimSpace
      collectionView.setCollectionViewLayout(layout, animated: true)
      collectionView.reloadData()
  
  }
  override func setSelected(_ selected: Bool, animated: Bool) {
      super.setSelected(selected, animated: animated)
  
      // Configure the view for the selected state
  }
      }
  
      extension GridViewCell{
  
  func setCollectionViewDataSourceDelegate&lt;D: UICollectionViewDataSource &amp; UICollectionViewDelegate&gt;(_ dataSourceDelegate: D, forRow row:Int){
  
      collectionView.delegate = dataSourceDelegate
      collectionView.dataSource = dataSourceDelegate
      collectionView.reloadData()
  
  }
  }
  </code></pre>
  
  <p>I think the <code>GridViewCell</code> which loads in the 2nd section of UITableview causing the problem.  But I've already added <code>dequeueReusableCellWithReuseIdentifier</code> in the <code>collectionView:cellForItemAtIndexPath:</code> method. So I'm clueless what's causing the error. </p>
  
  <p>Any help would be greatly appreciated.</p>