I am trying to accomplish the following task on my drawing app:

I have designed a custom UIView in a .xib file, consisting of only a 'close' button in the UIView. By default, I do not want my app to load this UIView; I would only like for it to load when I press a button on my app's main view. After the view pops up, I would like to still be able to access the other views on my app, while the pop up is still open. Particularly, I would still like to draw lines on the view I have set up as a 'canvas.' Currently, I have added three files for this custom pop up: a class file inherited from UIView called PopUpView.swift, another class file inherited from UIViewController called PopUpViewController.swift, and the .xib file. 

In the main ViewController, I have the following code

```
var popUp = popUpClass()    
@IBAction func showPopUp (sender: UIButton){
    self.view.addSubview(popUp)
    }

```

However, when I click on it, the view does not show up. I am a little confused about what the flow of the code should be and was wondering if anybody could offer me assistance?

Thank you!