title: Swift 3: Add UIButton extension to ViewController
body: <p>I'm a beginner in iOS/Swift and trying to create a simple application without Storyboard.
  I created a <code>UIButton</code> extension and I would like to add a simple button to my view (constraints will be set later). 
  Unfortunately the button is not visible.
  I would appreciate if somebody helps me.
  Thank you!</p>
  
  <p>--- Buttons.swift ---</p>
  
  <pre><code>extension UIButton {
  
  func createRectangleButton(buttonPositionX: Double, buttonPositionY: Double ,buttonWidth: Double, buttonHeight: Double, buttonTilte: String) {
      let button = UIButton(type: .system) as UIButton
      button.frame = CGRect(x: buttonPositionX, y: buttonPositionY, width: buttonWidth, height: buttonHeight)
      button.setTitle(buttonTilte, for: .normal)
      button.backgroundColor = COLOR_WHITE
      button.tintColor = COLOR_BLACK
      }   
  }
  </code></pre>
  
  <p>--- InitialViewController.swift ---</p>
  
  <pre><code>import UIKit 
  
  class InitialViewController: BaseViewController {
  
  override func viewDidLoad() {
      super.viewDidLoad()
  
      // Gradient Layer
      view.addGradientBackground(colorTop: COLOR_ROYALRED2, colorBottom: COLOR_ROYALRED1)
  
      // Button
      let startButton = UIButton()
      startButton.createRectangleButton(buttonPositionX: 50, buttonPositionY: 20, buttonWidth: 200, buttonHeight: 50, buttonTilte: "START")
      self.view.addSubview(startButton)
  
      }
  }
  </code></pre>