SwiftTipChildViewControllerUsingDestination.swift

override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
        
        switch segue.destination {
            
        case let viewController1 as ViewController1:
            self.viewController1 = viewController1
            
        case let viewController2 as ViewController2:
            self.viewController2 = viewController2
            
        case let viewController3 as ViewController3:
            self.viewController3 = viewController3
            
        default:
            break
        }
}