How to enable IBAction once numbers are entered into a UIText Field - ios

Question

I am quite new to a programming and I need a help.
I am trying to build a simple calculator. In nutshell: There are two UITextField where the numbers are inserted. There is IBAction (buttonCalculate) that performs the calculation + there is another IBAction (buttonClear) that clears the data inserted into text fields. Upon starting the application both IBAction buttons are disabled. The goal is to enable the IBAction (buttonCalculate) once numbers are inserted. In case the user inserts any other character then numbers a warning message(warrningSign2) needs to appear telling the user that ony numbers are accepted.
Can somebody give a tip / hint how I should proceed?
Thanks!
import UIKit
class ViewController: UIViewController {
#IBOutlet weak var Value: UITextField!
#IBOutlet weak var field1: UITextField!
#IBOutlet weak var field2: UITextField!
#IBOutlet weak var buttonClear: UIButton!
#IBOutlet weak var buttonCalculate: UIButton!
#IBOutlet weak var warrningSign: UITextField!
#IBOutlet weak var warrningSign2: UITextField!
func appLoad () {
buttonClear.isEnabled = false
buttonClear.backgroundColor = .gray
if field1.text == "" || field1.text == "" {
warrningSign.textColor = .red
butonCalculate.isEnabled = false
butonCalculate.backgroundColor = .gray}
}
override func viewDidLoad() {
super.viewDidLoad()
appLoad()
}
#IBAction func calculate(_ sender: Any) {
buttonClear.isEnabled = true
buttonClear.backgroundColor = UIColor(red: 74/255, green: 105/255, blue:187/255, alpha: 1)
Value.text = String(Float(field1.text!)! + Float(field2.text!)!)
}
#IBAction func Clear(_ sender: Any) {
Value.text = "Value"
self.field1.text = nil
self.field2.text = nil
}
}

Answer 1

Make UITextField(field1 and field2) Keyboard type to Number Pad or only acceptable number type.
You can catch the characters sent to a UITextField control by adding the below line:
textField.addTarget(self, action: #selector(textFieldDidChange), for: .editingChanged)
In textFieldDidChange delegate method you can get the text and validate as per your needs.
I would recommend to update the code like below,
#IBAction func calculate(_ sender: Any) {
calculateAction()
}
private func calculateAction() {
buttonClear.isEnabled = true
buttonClear.backgroundColor = UIColor(red: 74/255, green: 105/255, blue:187/255, alpha: 1)
Value.text = String(Float(field1.text!)! + Float(field2.text!)!)
}
And then call the calculateAction() in textFieldDidChange().