How to make textField validation code more compact and readable? - ios

Question

I am writing code for textField validation. The textField simply does not allow the user to write age other than 16..<80. I have written the code below and I feel it is poor in quality. Your suggestions to make below code more readable will be really helpful.
Setup:
Create textField and make a delegate to self.
extension UserProfileViewController: UITextFieldDelegate {
func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Bool {
let numberFiltered = string.components(separatedBy: NSCharacterSet(charactersIn: "0123456789").inverted).joined(separator: "")
guard string == numberFiltered, range.location < 2 else {
return false
}
if range.location==0, string.intValue == 0 {
return false
}
guard let textFieldValue = textField.text?.intValue, let currentValue = string.intValue else {
return true
}
let totalValue = textFieldValue*10 + currentValue
switch totalValue {
case 16..<80:
return true
default:
textField.text = ""
return false
}
}
}

Answer 1

Most of what you are doing is unnecessary. Just calculate what the new string would be, attempt to convert to an Int, and check the range.
func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Bool {
let oldText = textField.text!
let newText = oldText.replacingCharacters(in: Range(range, in: oldText)!, with: string)
if let num = Int(newText), num >= 16 && num < 70 {
return true
}
return false
}
FYI - Both uses of ! here are safe. UITextField text will never return nil and unless there is a serious bug in iOS, the range will be valid.