loginVC.swift

   
 import UIKit
import FBSDKLoginKit


class loginViewController: UIViewController , FBSDKLoginButtonDelegate {

    
    override func viewDidLoad() {
        
        super.viewDidLoad()
    
        // initializing the button
        let loginButton = FBSDKLoginButton()
        //adding the button to frame
        view.addSubview(loginButton)
        //specifying position of login button
        loginButton.frame = CGRect(x: 16, y: 50, width: view.frame.width  - 32, height: 50)
        // adding the delegate , also add the FBSDKLoginButtonDelegate to your class
        loginButton.delegate = self

    
    } //viewDidLoad
    
    
    func loginButtonDidLogOut(_ loginButton: FBSDKLoginButton!) {
        print("logout done")
    }
    
    
    func loginButton(_ loginButton: FBSDKLoginButton!, didCompleteWith result: FBSDKLoginManagerLoginResult!, error: Error!) {
        if (error != nil){
        print(error)
        }  //if
    
        else{
        print("login successful")
        } // else
    } //didCompleteWith

    
    
}