title: What does '!' (exclamation mark) next to the file name represent in Xcode
body: <h2>Issue:</h2>
  
  <p>I am wondering what does <strong>'!'  (exclamation mark)</strong>, next to the name of the file mean in <strong>Xcode</strong>. I know that it is meant to tell you that a file is <strong><em>"Missing"</em></strong>, but I couldn't find any online explanation. And I also need a way to fix it. I can edit the code inside of the so-called <strong><em>"Missing"</em></strong> file. When I run it into the simulator everything works completely fine, no error and not even a warning.</p>
  
  <h2>Technical Data:</h2>
  
  <p>I am running <strong>Xcode 8</strong> with <strong>Swift 3</strong>.</p>
  
  <h2>What I have tried so far:</h2>
  
  <ul>
  <li>I tried re-opening <strong><em>Xcode</em></strong> --> didn't work</li>
  <li>I tried solving it with <em>source-control</em> --> nothing happened</li>
  <li>I searched for it inside my <strong>trash</strong> --> no file inside the <strong>trash</strong>
  with the same name</li>
  <li>I have checked the <strong>connections</strong> --> <strong>everything is fine</strong></li>
  </ul>
  
  <h2>Images:</h2>
  
  <p><strong>1. The file inside my editor:</strong></p>
  
  <p><a href="https://i.stack.imgur.com/itB7v.png" rel="noreferrer"><img src="https://i.stack.imgur.com/itB7v.png" alt="enter image description here"></a></p>
  
  <p><strong>2. Simulator:</strong></p>
  
  <p><a href="https://i.stack.imgur.com/G0zVf.png" rel="noreferrer"><img src="https://i.stack.imgur.com/G0zVf.png" alt="enter image description here"></a></p>
  
  <h2>Code:</h2>
  
  <pre><code>import Foundation
  import UIKit
  
  class Documentation: UIViewController {
  
      @IBOutlet weak var Basics: UIButton!
      let defaults = UserDefaults.standard
  
      override func viewDidLoad() {
          super.viewDidLoad()
          self.view.addGestureRecognizer(self.revealViewController().panGestureRecognizer())
          let menuButton = UIBarButtonItem(barButtonSystemItem: .organize, target: self.revealViewController(), action: #selector(SWRevealViewController.revealToggle(_:)))
          menuButton.tintColor = UIColor.white
          self.navigationItem.leftBarButtonItem = menuButton
          self.customizeButton(button: Basics, angle: 50, borderWidth: 2, borderColor: #colorLiteral(red: 0.0693108514, green: 0, blue: 0.2353696823, alpha: 1))
  
      }
      @IBAction func BasicsAction(_ sender: UIButton) {
  
      }
  
      func customizeButton(button: UIButton, angle: Int, borderWidth: Int, borderColor: UIColor){
          button.layer.cornerRadius = CGFloat(angle)
          button.layer.borderWidth = CGFloat(borderWidth)
          button.layer.borderColor = borderColor.cgColor
          let completionLabel = button.viewWithTag(1) as! UILabel!
          completionLabel?.text = "0/10"
          if defaults.value(forKey: "\(button.currentTitle)") != nil{
              let done = defaults.value(forKey: "\(button.currentTitle)") as! Int
              completionLabel?.text = "\(done)/10"
              if done == 10{
                  button.layer.borderColor = #colorLiteral(red: 0.2193539292, green: 0.4209204912, blue: 0.1073316187, alpha: 1).cgColor
                  button.layer.borderWidth = 5
              }
          }
  
      }
  }
  </code></pre>
  
  <p>Any help is greatly appreciated if it comes with a good explanation!</p>