TextField Action After Done

Code Block 
import UIKit
class ViewController: UIViewController {
    @IBOutlet weak var textField: UITextField!
    
    override func viewDidLoad() {
        super.viewDidLoad()
        textField.delegate = self
        textField.returnKeyType = .done
    }
}
extension ViewController: UITextFieldDelegate {
    func textFieldShouldReturn(_ textField: UITextField) -> Bool {
        print(#function)
        textField.resignFirstResponder()
        //Do something...
        return true
    }
}

Does it have to be TextFieldShouldReturn

can there be another function if I want to add another textfield?

 is there another function other then textFieldShouldReturn()?

Code Block 
func textFieldShouldReturn(_ textField: UITextField) -> Bool {
  textField.resignFirstResponder()
  let text = textField.text
  let textNum = Int(text!)
  /*when you enter a value it will affect, the slider and squareOne width value will change and squareTwo width will change */
  if widthPer.text == text {
    squareOneWidth.constant = CGFloat(textNum!) * 2
    slider.value = Float(textNum!)
    calPercentage()
    calPercentageTwo()
    /*when you enter a value it will affect, the sliderHeight and squareOne height will change and squareTwo height will change */
  } else if heightPer.text == text {
    calPercentage()
    calPercentageTwo()
  }
  print("\(text)")
  return true
}

 It says my text value is nil and it does not move the slider.

I know there is a lot of details

Code Block 
func textFieldShouldReturn(_ textField: UITextField) -> Bool {
  textField.resignFirstResponder()
  let text = textField.text
  let textNum = Int(text!)
  if widthPer.text == text {
    slider.value = Float(textNum!)
  } 
return true
}

the textField returns nil

It says found nil while unwrapping an optional value. slider.value = Float(textNum!),

Code Block 
func textFieldShouldEndEditing(_ textField: UITextField) -> Bool {
    // Make sure the user entered a number
  let num = Double(textField.text!)
  if num! < 10 {
      textField.text = "10%"
  } else if num! > 90 {
      textField.text = "90%"
  } else if num! >= 10 || num! <= 90 {
      textField.text = String(Int(num!)) + "%"
  }
  //print(num!)
  return true
}

I am trying to allow the textField I have to accept an Int that moves a slider, I can get it to work by commenting out my function that only allows values from 10 to 90.