How to limit the textfield entry to 2 decimal places in swift 4?

Question

I have a textfield and I want to limit the entry to max 2 decimal places.

number like 12.34 is allowed but not 12.345

How do I do it?

Answer 1

Swift 5. Adding to Enrique's answer (based on Code Different baseline), I found the need to allow the Delete key to operate anywhere on the line along with a sign (+ or -) or decimal point at the beginning of the input line.

func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Bool {
    // Limit number fields to +/- Real #s: sign as first character, one decimal separator, one decimal place after separator
    if string.isEmpty { return true }   // Allow delete key anywhere!
    guard let oldText = textField.text, let rng = Range(range, in: oldText) else {
        return true
    }
    let newText = oldText.replacingCharacters(in: rng, with: string)

    let isNumeric = newText.isEmpty || (Double(newText) != nil)

    let formatter = NumberFormatter()
    formatter.locale = .current
    let decimalPoint = formatter.decimalSeparator ?? "."
    let numberOfDots = newText.components(separatedBy: decimalPoint).count - 1

    let numberOfDecimalDigits: Int
    if let dotIndex = newText.firstIndex(of: ".") {
        numberOfDecimalDigits = newText.distance(from: dotIndex, to: newText.endIndex) - 1
    } else {
        numberOfDecimalDigits = 0
    }
    if newText.count == 1 && !isNumeric {   // Allow first character to be a sign or decimal point
        return CharacterSet(charactersIn: "+-" + decimalPoint).isSuperset(of: CharacterSet(charactersIn: string))
    }
    return isNumeric && numberOfDots <= 1 && numberOfDecimalDigits <= 1
}