Why my label left 1 character when updating UILabel from UITextField? - ios

Question

so I am making UILabel live update from UiTextfield (user input). I am using the code from this thread Swift3: Live UiLabel update on user input
but somehow, my UILabel always left one character when I fully erase the text in my UITextField. like the .gif in here http://g.recordit.co/SPQWnYtHJg.gif
and it seems one character is always missing like the picture below
here is the code I use
import UIKit
class CreateEventVC: UIViewController {
#IBOutlet weak var eventNameTextField: UITextField!
#IBOutlet weak var eventNameLabel: UILabel!
override func viewDidLoad() {
super.viewDidLoad()
//initial value
eventNameLabel.text = " "
// delegate declaration
eventNameTextField.delegate = self
}
}
extension CreateEventVC : UITextFieldDelegate {
func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Bool {
eventNameLabel.text = eventNameTextField.text
return true
}
}
I initially suspect because I add this line in viewDidload
eventNameLabel.text = " "
but if i delete this one, the problem is still there
what should I do ?

Answer 1

textField:shouldChangeCharactersIn:range:replacementString is called before the change is applied to the text field, this allows your app to veto the request and filter out unwanted content.
The problem is, you're relying on the text field's text. Instead, you need build the resulting value from the information passed to the delegate and apply that
Maybe something more like...
extension CreateEventVC: UITextFieldDelegate {
func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Bool {
let text = textField.text ?? ""
eventNameLabel.text = (text as NSString).replacingCharacters(in: range, with: string)
return true;
}
}

Answer 2

class CreateEventVC: UIViewController {
#IBOutlet weak var eventNameTextField: UITextField!
#IBOutlet weak var eventNameLabel: UILabel!
override func viewDidLoad() {
super.viewDidLoad()
//initial value
eventNameLabel.text = " "
eventNameTextField.addTarget(self, action: #selector(onTextFieldTextDidChange), for: .editingChanged)
}
#objc func onTextFieldTextDidChange() {
eventNameLabel.text = eventNameTextField.text
}
}
Explanations:
We add target to the eventNameTextField which will call the onTextFieldTextDidChange func each time the textField text is changed.