title: QLPreviewController not work on iOS11
body: <pre><code>class ViewController: UIViewController {
      let quickLookController = QLPreviewController()
  
      override func viewDidLoad() {
          super.viewDidLoad()
  
          quickLookController.dataSource = self
          quickLookController.delegate = self
      }
  
      @IBAction func buttonAction(_ sender: Any) {
          present(quickLookController, animated: true, completion: nil)
  
          quickLookController.reloadData()
          quickLookController.refreshCurrentPreviewItem()
      }
  }
  
  extension ViewController: QLPreviewControllerDataSource,QLPreviewControllerDelegate {
  
      func numberOfPreviewItems(in controller: QLPreviewController) -&gt; Int {
          return 1
      }
  
      func previewController(_ controller: QLPreviewController, previewItemAt index: Int) -&gt; QLPreviewItem {
          let path = Bundle.main.path(forResource: "AppCoda-Ppt.ppt", ofType: nil)
  
          let url = NSURL(fileURLWithPath: path!)
  
          return url
      }
  }
  </code></pre>
  
  <p><img src="https://i.stack.imgur.com/sMXAf.png" alt="enter image description here"></p>