Storyboard uiviewcontroller, 'custom class' not showing in drop down

If you still have your problem or for those who could have the same problem:

Make sure to select on your storyboard your "ViewController" instead of your "View" (which is automatically selected when you click on the view in the storyboard). The difference between those two is that when the view controller is selected, a blue rectangle pop up around your app. To be sure to select the view controller, open the document outline and select it directly in your storyboard hierarchy.

Two ways I found that solve the problem but they are work arounds:-

1. Just type the view controllers name in the text field, or
2. close the project and then reopen it and in the project initialization it places the file on the list.