Accounting for backspace in UITextField validation using shouldChangeCharactersInRange

Question

I'm attempting to put validation in a textField to ensure it only contains letters. It works until I press backspace.

As a workaround, I tried to create a NSMutableCharacterSet and use formUnionWithCharacterSet to add NSCharacterSet.letterCharacterSet(). Then I added backspace to it. That's not working either.

func textField(textField: UITextField, shouldChangeCharactersInRange range: NSRange, replacementString string: String) -> Bool {        
    // Limit to Letters & Backspace
    // let charactersAllowed = NSCharacterSet.letterCharacterSet()
    let charactersAllowed = NSMutableCharacterSet()
    charactersAllowed.formUnionWithCharacterSet(NSCharacterSet.letterCharacterSet())
    charactersAllowed.addCharactersInString("\\b")

    if let rangeOfCharactersAllowed = string.rangeOfCharacterFromSet(charactersAllowed, options: .CaseInsensitiveSearch) {
        return rangeOfCharactersAllowed.count == string.characters.count
    } else {
        displayAlert("Invalid Character", alertMessage: "Please enter only letters")
        return false
    }
}

I've found some old crusty answers in Objective-C, but none of them seem to work for me. Any other suggestions for going to NSMutableCharacterSet route for validation?

If it helps, I'm using the simulator and attempting to press the backspace key (delete) in the upper-right-hand corner of the keyboard.

See https://developer.apple.com/library/ios/documentation/UIKit/Reference/UIKeyInput_Protocol/#//apple_ref/occ/intfm/UIKeyInput/deleteBackward — danh, Jul 17 '16 at 15:04
@danh Thank you. I'll set about figuring out what to do with it. — Adrian, Jul 17 '16 at 15:16

score 2 · Accepted Answer · edited Jul 17 '16 at 21:34

2

Try this:

func textField(textField: UITextField, shouldChangeCharactersInRange range: NSRange, replacementString string: String) -> Bool {
  let notLetterSet = NSCharacterSet.letterCharacterSet().invertedSet
  let textFieldInvalidCharPosition = string.rangeOfCharacterFromSet(notLetterSet)

if (textFieldInvalidCharPosition != nil) {
     return false
  } else {
     return true
  }
}

edited Jul 17 '16 at 21:34

Adrian

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answered Jul 17 '16 at 16:11

meowmeowmeow

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Accounting for backspace in UITextField validation using shouldChangeCharactersInRange

1 Answers1