Present Modal ViewController when tap a TabBarItem (like camera VC in Instagram)

gistfile1.swift

// 1. First Create a Dummy UIViewController that has a root relation with the UITabBarController
// 2. Make this controller implement a UITabBarControllerDelegate
// 3. In ViewDidLoad:
  override func viewDidLoad() {
    super.viewDidLoad()
    self.tabBarController?.delegate = self
  }
// 4. Implement this delegate method:
  func tabBarController(tabBarController: UITabBarController, didSelectViewController viewController: UIViewController) {
    let isModalTab = viewController == self
    
    if isModalTab {
      let cameraVC = UIStoryboard.cameraVC() // 5. HERE YOU SPECIFY THE MODAL VIEW CONTROLLER!!!
      self.presentViewController(cameraVC, animated: true, completion: nil)
    }
  }
// 5. That's all