How to create extension file and call it in View Controller in iOS Swift 3?

Question

I have made extension file like this :

import Foundation
import Swift
import UIKit

extension UIButton{
func sayHello() {
        print("Hello bro...")
    }
}  

and Then call sayHello method in view controller like this:

override func viewDidLoad() {
        super.viewDidLoad()
        sayHello()  
    }

But show this error:

I think this problem accrued because of iron importing of extension file in view controller.
Please help me.
Thank you.

Answer 1

Your implementation is wrong. You are creating extension of UIButton and calling a method on UIViewController .

extension UIViewController {
func sayHello() {
        print("Hello bro...")
    }
} 

If you want to create a UIButton extension

 extension UIButton {
    func sayHello() {
            print("Hello bro...")
        }
    } 

then you will need to call it on UIButton like below

let button = UIButton()
button.sayHello()

Answer 2

use extension UIViewController not use UIButton

below code extend UIButton so

someButton.sayHello() is works

extension UIButton {
    func sayHello() {
        print("Hello bro...")
    }
}  

if you want use in viewDidLoad() of UIViewController extend UIViewController instead UIButton

extension UIViewController {
    func sayHello() {
        print("Hello bro...")
    }
}

it works in 'viewDidLoad'

this is some example extension to call alert

ex)

extension UIViewController {
    func alert(title: String, message: String) {
        let alertController = UIAlertController(title: title, message: message, preferredStyle: .alert)
        alertController.view.tintColor = .black
        let someAction = UIAlertAction(title: "Some", style: .default, handler: nil)
        //let alertController.addAction(someAction)
        alertController.addAction(someAction)
        self.present(alertController, animated: true, completion: nil)
    }
}