How to disable(deactivate) button while program is running?

Question

I have a TextField and a button. This TextField is limited up to 3 which can take 3 letters or numbers.

Here is my question. When the program is running, if this textfield is empty or if this textfield doesnt contains only numbers, i want my button as disable. Can you help me about this code?

import UIKit


class ViewController: UIViewController, UITextFieldDelegate{
    @IBOutlet var VizeGir: UITextField!



    @IBOutlet var SonucLabel: UILabel!

    @IBOutlet var SonucLabel2: UILabel!


    @IBOutlet var SonucLabel3: UILabel!


    @IBOutlet var SonucLabel4: UILabel!


    @IBOutlet var SonucLabel5: UILabel!
    @IBOutlet weak var Hes: UIButton!

    @IBAction func Hesapla(sender: AnyObject) {

        let vize = Float(VizeGir.text!)!
        var final: Float
        var vize2: Float
        var sonuc: Float
        var aa,ab,ba,bb,c:Int

        if VizeGir.text!.isEmpty {
            print("Nothing to see here")
        }
        if vize<0 || vize>100{
            SonucLabel.text = "Yanlış değer girdiniz."
            SonucLabel5.text = " "
            SonucLabel4.text = " "
            SonucLabel3.text = " "
            SonucLabel2.text = " "
            SonucLabel.textColor = UIColor(red: 255/255.0, green: 0/255.0, blue: 0/255.0, alpha: 1.0)
        }else{
            vize2 = (vize / 100) * 40
            sonuc = 90
            final = sonuc - vize2
            aa = Int(final / 60 * 100)
            if aa<50 || aa>100{
            SonucLabel.text = "A1 Alamazsınız."
            SonucLabel.textColor = UIColor(red: 255/255.0, green: 0/255.0, blue: 0/255.0, alpha: 1.0)
            }else{
            SonucLabel.text = "A1 almanız için gereken not: \(aa)"
            SonucLabel.textColor = UIColor(red: 46/255.0, green: 204/255.0, blue: 113/255.0, alpha: 1.0)}
            sonuc = 80
            final = sonuc - vize2
            ab = Int(final / 60 * 100)
            if ab<50 || ab>100{
            SonucLabel2.text = "A2 Alamazsınız."
            SonucLabel2.textColor = UIColor(red: 255/255.0, green: 0/255.0, blue: 0/255.0, alpha: 1.0)
            }else{
            SonucLabel2.text = "A2 almanız için gereken not: \(ab)"
            SonucLabel2.textColor = UIColor(red: 46/255.0, green: 204/255.0, blue: 113/255.0, alpha: 1.0)
            }
            sonuc = 70
            final = sonuc - vize2
            ba = Int(final / 60 * 100)
            if ba<50 || ba>100{
            SonucLabel3.text = "B1 Alamazsınız."
            SonucLabel3.textColor = UIColor(red: 255/255.0, green: 0/255.0, blue: 0/255.0, alpha: 1.0)
            }else{
            SonucLabel3.text = "B1 almanız için gereken not: \(ba)"
            SonucLabel3.textColor = UIColor(red: 46/255.0, green: 204/255.0, blue: 113/255.0, alpha: 1.0)
            }
            sonuc = 65
            final = sonuc - vize2
            bb = Int(final / 60 * 100)
            if vize == 98 || vize == 97 || vize == 96 || vize == 95 || vize == 94 || vize == 93 || vize == 92 || vize == 91 || vize == 90 || vize == 89 || vize == 88 || vize == 87 {
            SonucLabel4.text = "B2 almanız için gereken not: 50"
            SonucLabel4.textColor = UIColor(red: 46/255.0, green: 204/255.0, blue: 113/255.0, alpha: 1.0)
            }else if vize == 12{
                SonucLabel4.text = "B1 almanız için gereken not: 100"
                SonucLabel4.textColor = UIColor(red: 46/255.0, green: 204/255.0, blue: 113/255.0, alpha: 1.0)}
            else if bb<=50 || bb>=100 {
                SonucLabel4.text = "B2 Alamazsınız."
                SonucLabel4.textColor = UIColor(red: 255/255.0, green: 0/255.0, blue: 0/255.0, alpha: 1.0)}
            else{
                SonucLabel4.text = "B2 almanız için gereken not: \(bb)"
                SonucLabel4.textColor = UIColor(red: 46/255.0, green: 204/255.0, blue: 113/255.0, alpha: 1.0)
            }
            sonuc = 60
            final = sonuc - vize2
            c = Int(final / 60 * 100)
            if vize==86 || vize==85 || vize==84 || vize==83 || vize==82 || vize==81 || vize==80 || vize==79 || vize==78 || vize==77 || vize==76{
                SonucLabel5.text = "C almanız için gereken not: 50"
                SonucLabel5.textColor = UIColor(red: 46/255.0, green: 204/255.0, blue: 113/255.0, alpha: 1.0)
            }
            else if c<50 || c>100{
                SonucLabel5.text = "C alamazsınız."
                SonucLabel5.textColor = UIColor(red: 255/255.0, green: 0/255.0, blue: 0/255.0, alpha: 1.0)
            }
            else{
                SonucLabel5.text = "C almanız için gereken not: \(c)"
                SonucLabel5.textColor = UIColor(red: 46/255.0, green: 204/255.0, blue: 113/255.0, alpha: 1.0)
            }


        }

                }


    override func viewDidLoad() {
        super.viewDidLoad()
        VizeGir.delegate = self
            }

    func textField(textField: UITextField, shouldChangeCharactersInRange range: NSRange,
        replacementString string: String) -> Bool
    {
        let maxLength = 3
        let currentString: NSString = VizeGir.text!
        let newString: NSString =
        currentString.stringByReplacingCharactersInRange(range, withString: string)
        return newString.length <= maxLength        
    }

    func initializeTextFields() {
        VizeGir.delegate = self
        VizeGir.keyboardType = UIKeyboardType.NumberPad
    }


    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }


}

Answer 1

You need to check each time a character is entered to your textField what characters the string contains and if it contains any characters.

Complete code with comments:

class ViewController: UIViewController, UITextFieldDelegate {

    @IBOutlet weak var buttonOk: UIButton!

    override func viewDidLoad() {
        super.viewDidLoad()
    }
    @IBAction func textField_EditingChanged(sender: UITextField) {
        // Check the length
        if sender.text?.characters.count == 0{
            buttonOk.enabled = false
        }
        else{
            buttonOk.enabled = true
        }

        // Check if numeric or not
        if let number = Int(sender.text!)
        {
            print("Number")
            buttonOk.enabled = true
        }
        else
        {
            print("Not number")
            buttonOk.enabled = false
        }
    }
}