uiOperation.swift

import Foundation

class UIOperation: AsyncOperation {
    let viewController: UIViewcontroller!
  
    override func execute() {
        let alert = UIAlertController(title: "My Alert", message: @"This is an alert.", preferredStyle: .alert) 
        alert.addAction(UIAlertAction(title: "OK", style: .`default`, handler: { _ in 
              self.handleInput()
        }))
        viewController.present(alert, animated: true, completion: nil) 
    }
  
    func handleInput() {
        //do something and continue operation
    }
  
}