title: CollectionView not display data after parsing JSON
body: <p>After parsing JSON I got my data in arraOfData of ViewController, but collectionView not display this. If I use static array all working. 
  collectionview.reloadData() is not working. In my opinion, need somehow waiting data from parsing, then try load collectionView. I tried use refresherControler for waiting data, but I don't know where put method "endRefreshing" (i guess startRefreshing need in ViewDidLoad)
  If I use reloadData like didSet in arraOfData
  I got error cause collectionView is nil. Use reloadData right after got data from parsing same didn't work for me
  And a big request to tell a couple of resources (articles) on this topic, I feel that I have big problems with displaying data and in what sequence functions start to load. Thanks a lot.</p>
  
  <pre><code>class ViewController: UIViewController {
  
  
  @IBOutlet weak var collectionView: UICollectionView!
  
  
  var arraOfData = [GettingMoney]() {
      didSet {
          print("Changes: \(arraOfData.count)")
      }
  }
  
  //  let arr = ["1", "2", "3"] - test, if i use this array, collectionView display data
  
    override func viewDidLoad() {
      super.viewDidLoad()
      GettingMoney.fetchData()
  
      collectionView.dataSource = self
      collectionView.delegate = self
  
    }
  
  }
  
  extension ViewController: UICollectionViewDelegate, 
     UICollectionViewDataSource {
  func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -&gt; Int {
      return arraOfData.count
  }
  
    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -&gt; UICollectionViewCell {
      let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "collectionCellId", for: indexPath) as? CollectionViewCell
      cell?.currentCurrency.text = "\(arraOfData[indexPath.row])"
      return cell!
  
    }
  }
  </code></pre>