How to limit the number of characters in a UITextField or UITextView

Swift version: 5.6

Paul Hudson @twostraws September 19th 2019

If you have a UITextField or UITextView and want to stop users typing in more than a certain number of letters, you need to set yourself as the delegate for the control then implement either shouldChangeCharactersIn (for text fields) or shouldChangeTextIn (for text views).

Next, add one of these two methods, depending on whether you are working with text fields (single line) or text views (multiple lines):

// Use this if you have a UITextField
func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Bool {
    // get the current text, or use an empty string if that failed
    let currentText = textField.text ?? ""

    // attempt to read the range they are trying to change, or exit if we can't
    guard let stringRange = Range(range, in: currentText) else { return false }

    // add their new text to the existing text
    let updatedText = currentText.replacingCharacters(in: stringRange, with: string)

    // make sure the result is under 16 characters
    return updatedText.count <= 16
}

// Use this if you have a UITextView
func textView(_ textView: UITextView, shouldChangeTextIn range: NSRange, replacementText text: String) -> Bool {
    // get the current text, or use an empty string if that failed
    let currentText = textView.text ?? ""

    // attempt to read the range they are trying to change, or exit if we can't
    guard let stringRange = Range(range, in: currentText) else { return false }

    // add their new text to the existing text
    let updatedText = currentText.replacingCharacters(in: stringRange, with: text)

    // make sure the result is under 16 characters
    return updatedText.count <= 16
}

I've specified 16 as the maximum number of characters, but just change that to whatever you need.