Detect backspace Event in UITextField

Question

I am searching for solutions on how to capture a backspace event, most Stack Overflow answers are in Objective-C but I need on Swift language.

First I have set deleg

Answer 1

Swift 4

func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Bool {

            let  char = string.cString(using: String.Encoding.utf8)!
            let isBackSpace = strcmp(char, "\\b")

            if isBackSpace == -92 {
                print("Backspace was pressed")
                return false
            }
}

Answer 2

I implemented this feature:

And in the case where the last textFiled is empty, I just want to switch to the previous textFiled. I tried all of the answers above, but no one works fine in my situation. For some reason, if I add more logic than print in isBackSpace == -92 parentheses block this method just stopped work...

As for me the method below more elegant and works like a charm:

Swift

class YourTextField: UITextField {

    // MARK: Life cycle

    override func awakeFromNib() {
        super.awakeFromNib()
    }

    // MARK: Methods

    override func deleteBackward() {
        super.deleteBackward()

        print("deleteBackward")
    }

}

Thanks @LombaX for the answer

Answer 3

I prefer subclassing UITextField and overriding deleteBackward() because that is much more reliable than the hack of using shouldChangeCharactersInRange:

class MyTextField: UITextField {
    override public func deleteBackward() {
        if text == "" {
             // do something when backspace is tapped/entered in an empty text field
        }
        // do something for every backspace
        super.deleteBackward()
    }
}

The shouldChangeCharactersInRange hack combined with an invisible character that is placed in the text field has several disadvantages:

• with a keyboard attached, one can place the cursor before the invisible character and the backspace isn't detected anymore,
• the user can even select that invisible character (using Shift Arrow on a keyboard or even by tapping on the caret) and will be confused about that weird character,
• the autocomplete bar offers weird choices as long as there's only this invisible character,
• Asian language keyboards that have candidate options based on the text field's text will be confused,
• the placeholder isn't shown anymore,
• the clear button is displayed even when it shouldn't for clearButtonMode = .whileEditing.

Of course, overriding deleteBackward() is a bit inconvenient due to the need of subclassing. But the better UX makes it worth the effort!

And if subclassing is a no-go, e.g. when using UISearchBar with its embedded UITextField, method swizzling should be fine, too.

Answer 4

Swift 4

I find the comparison using strcmp irrelevant. We don't even know how strcmp is operating behind the hoods.In all the other answers when comparing current char and \b results are -8 in objective-C and -92 in Swift. I wrote this answer because the above solutions did not work for me. ( Xcode Version 9.3 (9E145) using Swift 4.1 )

FYI : Every character that you actually type is an array of 1 or more elements in utf8 Encoding. backSpace Character is [0]. You can try this out.

PS : Don't forget to assign the proper delegates to your textFields.

public func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Bool {

    let  char = string.cString(using: String.Encoding.utf8)!
    if (char.elementsEqual([0])) {
        print("Backspace was pressed")
    }
    else {
        print("WHAT DOES THE FOX SAY ?\n")
        print(char)
    }
    return true
}

Answer 5

Swift 4.2

func textField(textField: UITextField, shouldChangeCharactersInRange range: NSRange, replacementString string: String) -> Bool {
    if let char = string.cString(using: String.Encoding.utf8) {
        let isBackSpace = strcmp(char, "\\b")
        if (isBackSpace == -92) {
            print("Backspace was pressed")
        }
    }
    return true
}

Older Swift version

func textField(textField: UITextField, shouldChangeCharactersInRange range: NSRange, replacementString string: String) -> Bool {
    let  char = string.cStringUsingEncoding(NSUTF8StringEncoding)!
    let isBackSpace = strcmp(char, "\\b")

    if (isBackSpace == -92) {
        println("Backspace was pressed")
    }
    return true
}

Answer 6

If u need detect backspace even in empty textField (for example in case if u need auto switch back to prev textField on backSpace pressing), u can use combination of proposed methods - add invisible sign and use standard delegate method textField:shouldChangeCharactersInRange:replacementString: like follow

1. Create invisible sign

   private struct Constants {
       static let InvisibleSign = "\u{200B}"
   }
   

2. Set delegate for textField

   textField.delegate = self
   

3. On event EditingChanged check text and if needed add invisible symbol like follow:

   @IBAction func didChangeEditingInTextField(sender: UITextField) {
       if var text = sender.text {
           if text.characters.count == 1 && text != Constants.InvisibleSign {
               text = Constants.InvisibleSign.stringByAppendingString(text)
               sender.text = text
           }
       }
   }
   

4. Add implementation of delegate method textField:shouldChangeCharactersInRange:replacementString:

   extension UIViewController : UITextFieldDelegate {
       // MARK: - UITextFieldDelegate
       func textField(textField: UITextField, shouldChangeCharactersInRange range: NSRange, replacementString string: String) -> Bool {
   
           let  char = string.cStringUsingEncoding(NSUTF8StringEncoding)!
           let isBackSpace = strcmp(char, "\\b")
   
           if (isBackSpace == -92) {
               if var string = textField.text {
                   string = string.stringByReplacingOccurrencesOfString(Constants.InvisibleSign, withString: "")
                   if string.characters.count == 1 {
                       //last visible character, if needed u can skip replacement and detect once even in empty text field
                       //for example u can switch to prev textField 
                       //do stuff here                            
                   }
               }
           }
           return true
       }
   }