Detecting a specific key [specifically the back/ return/ delete key] on the iPhone keyboard in swift

Question

Before I get asked, no this is not a duplicate. No other question addresses this that I found with a satisfying answer.

I have been working on some code to make a data interface and I didn't want to use a date picker.

This is the code I'm using to get the XX/XX/XX format:

extension OneCreateAccountViewController {
    func textFieldDidChangeSelection(_ textField: UITextField) {
        
        if textField.placeholder == "DD/MM/YY" {

            
            if textField.text!.count >= 2 && textField.text!.count < 3  {

                textField.text! = "\(textField.text!)/"

            } else {
                
                if textField.text!.count >= 5 && textField.text!.count < 6   {

                    textField.text! = "\(textField.text!)/"

                } else {
                    
                    if textField.text!.count >= 9 {
                        
                        textField.text!.removeLast()
                   
                    }
                }
            }
        }
    }
}

As you can see it is pretty barebones, but my issue is that once "/" is inserted, no matter what happens, you cannot remove using the return key. I want a specific else statement that would work something like "else - if the backspace is returned and the last character is "", delete that character."

please help me in SPECIFICALLY HAVING A CODE THAT REGISTERS THE RETURN KEY (even if it is a simple "if return is pressed, print ("Hi")" like answer.)

Answer 1

You will have a lot of trouble trying to do this with only textFieldDidChangeSelection ...

To answer your specific "CODE THAT REGISTERS THE RETURN KEY" question, implement textFieldShouldReturn in your UITextFieldDelegate:

extension OneCreateAccountViewController: UITextFieldDelegate {
    
    func textFieldShouldReturn(_ textField: UITextField) -> Bool {
        print("Enter key pressed")
        // Handle Enter key processing here
        return true
    }
    
}

To detect Backspace, implement shouldChangeCharactersIn:

extension OneCreateAccountViewController: UITextFieldDelegate {
    
    func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Bool {
        
        if string.isEmpty {
            print("Backspace detected")
            // Handle any additional backspace processing here
        }

        return true

    }
    
    func textFieldShouldReturn(_ textField: UITextField) -> Bool {
        print("Enter key pressed")
        // Handle Enter key processing here
        return true
    }
    
}

---

Important note!! - that will fail due to a bug in the iOS simulators! It does work on an iOS 15.0 simulator, and I've seen notes that the bug is fixed in iOS 17.4 simulator.

---

For the simplest approach, handle each new input in shouldChangeCharactersIn:

extension OneCreateAccountViewController: UITextFieldDelegate {
    
    func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Bool {
        
        // get the current text from the text field
        //  set it to "" if the text field is empty
        var theText = textField.text ?? ""
        
        if string.isEmpty {
            print("Backspace detected")
            // if the text field is empty, just ignore
            if theText.count == 0 {
                return false
            }
            // remove the last character from the string
            theText.removeLast()
            // if the string was, for example, "12/1"
            //  it will now be "12/"
            //  so remove the trailing slash
            if theText.last == "/" {
                theText.removeLast()
            }
            // update the text field
            textField.text = theText
            
            // don't allow built-in processing
            return false
        }
        
        // it wasn't backspace
    
        // if it's not a digit, or we already have 8 characters ("nn/nn/nn"), discard the new input
        if theText.count == 8 || !"0123456789".contains(string) {
            return false
        }
        
        // if the current text is "nn" or "nn/nn"
        //  append a slash
        if theText.count == 2 || theText.count == 5 {
            theText += "/"
        }
        // append the new input
        theText += string
        
        // update the text field
        textField.text = theText
        
        // don't allow built-in processing
        return false
        
    }
    
    func textFieldShouldReturn(_ textField: UITextField) -> Bool {
        
        print("Enter key pressed")
        // Handle Enter key processing here
        return true
        
    }
    
}

Your task will be, however, rather more complex...

For example, suppose the user has typed 25/12/2 and moves the caret / insertion point:

What should happen if a 0 is typed? Or a backspace? Do you want to insert/delete where the caret is, reformat the slashes if necessary, maintain the caret location, and so on.

---

And what do you want to happen if the user types 98/76/54?

Ideally (I expect) you will want to validate every "keystroke":

• if it's the first character
  • allow only 0, 1, 2 or 3
• if it's the 2nd character
  • allow 1-9 if first char is 0
  • allow 0-9 if the first char is 1 or 2
  • allow 0 or 1 if the first char is 3
• if it's the 4th character (immediately following the first slash)
  • allow only 0 or 1
• if it's the 5th character
  • allow 1-9 if fourth char is 0
  • allow 0, 1 or 2 if the fourth char is 1

and so on.

Of course, if the user types 02/3 or 06/31 or 05/38 (etc), you'll also need to reject that last input.