textField allowing all characters despite ShouldChangeCharactersIn function - swift

Question

As I'm trying to internalize code I've been using for years (without much understanding), I've created my version that in theory should copy its purpose.
I have a textField in which I'm only allowing decimal numbers and one period - ".". However, at the moment, my textField is allowing any character to be entered.
I have imported the UITextFieldDelegate class, connected my UITextField as an outlet, and set my textfield to the textFieldDelefate in viewDidLoad.
func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Bool {
//characterSet that holds digits
var allowed = CharacterSet.decimalDigits
//initialize the period for use as a characterSet
let period = CharacterSet.init(charactersIn: ".")
//adding these two characterSets together
allowed.formUnion(period)
//all the characters not in the allowed union
let inverted = allowed.inverted
//if latest input is from the characters not allowed is present (aka, empty), do not change the characters in the text range
if string.rangeOfCharacter(from: inverted) != nil
{
return false
}
//if the text already contains a period and the string contains one as well, do not change output
else if (textField.text?.contains("."))! && string.contains(".")
{
return false
}
//however, if not in the inverted set, allow the string to replace latest value in the text
else
{
return true
}
This function is not disabling the more than one period and invert of decimal numbers.

Answer 1

I seems to work for me, I moved some of the character setup into some lazy vars so that it is only done once, and not every time the delegate is called.
import UIKit
class ContainerController: UIViewController, UITextFieldDelegate {
#IBOutlet weak var textField: UITextField!
//characterSet that holds digits
lazy var allowed:CharacterSet = {
var allowed = CharacterSet.decimalDigits
//initialize the period for use as a characterSet
let period = CharacterSet.init(charactersIn: ".")
//adding these two characterSets together
allowed.formUnion(period)
return allowed
}()
lazy var inverted:CharacterSet = {
return allowed.inverted
}()
override init(nibName nibNameOrNil: String?, bundle nibBundleOrNil: Bundle?) {
super.init(nibName: nibNameOrNil, bundle: nibBundleOrNil)
}
required init?(coder aDecoder: NSCoder) {
super.init(coder: aDecoder)
}
override func viewDidLoad() {
super.viewDidLoad()
textField.delegate = self
}
func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Bool {
print("shouldChangeCharactersIn", range)
print("replacementString", string)
//if latest input is from the characters not allowed is present (aka, empty), do not change the characters in the text range
if string.rangeOfCharacter(from: inverted) != nil {
return false
} else if (textField.text?.contains("."))! && string.contains(".") {
//if the text already contains a period and the string contains one as well, do not change output
return false
} else {
//however, if not in the inverted set, allow the string to replace latest value in the text
return true
}
}
}