allow only letters for User Name - swift3

Question

I'm trying to limit the users First_Name to allow only letters so it should respond with an error for numbers or special characters after clicking on send_button. I found some examples here but because they are build on older swift version I'm having problems to make it work. Until now I've managed to read the First Name and throw an error if the first element on this textfield is not a letter but the code allow things like this (First name = "J123g") or ("Mark##$") and I don't want this to be the case.
func isOneLetter(in text: String) -> Bool {
do {
let regex = try NSRegularExpression(pattern: "[a-zA-Z]")
let nsString = text as NSString
let results = regex.matches(in: text, range: NSRange(location: 0, length: nsString.length))
let temp = results.map { nsString.substring(with: $0.range)}
return temp.isEmpty
} catch let error {
print("invalid regex: \(error.localizedDescription)")
return false
}
}
#IBAction func Send_Button(_ sender: AnyObject) {
let UserName = First_Name.text
if (isOneLetter(in: UserName!))
{
DisplayMyAlertMessage(userMessage: "First Name must contain only letter and spaces")
}
}

Answer 1

Your regex pattern checks for one alphanumeric character which matches both unwanted examples.
This regex checks for from beginning (^) to the end ($) of the string there must be one or more (+) alphanumeric characters ([a-zA-Z]). The benefit is that it treats an empty string also as bad.
^[a-zA-Z]+$

Answer 2

1st you have to inherit the UITextViewDelegate class with you own
class
class ViewController: UIViewController, UITextViewDelegate {
2nd add an IBOutlet
#IBOutlet weak var firstName: UITextField!
3rd you have to assure this object is using
override func viewDidLoad() {
super.viewDidLoad()
firstName.delegate = self
}
func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Bool {
if textField == firstName {
let allowedCharacters = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz"
let allowedCharacterSet = CharacterSet(charactersIn: allowedCharacters)
let typedCharacterSet = CharacterSet(charactersIn: string)
let alphabet = allowedCharacterSet.isSuperset(of: typedCharacterSet)
return alphabet
}
}

Answer 3

Another way could be:
let userInput = ""
let set = CharacterSet(charactersIn: "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLKMNOPQRSTUVWXYZ")
if userInput.rangeOfCharacter(from: set.inverted) != nil {
print("ERROR: There are numbers included!")
}

Answer 4

Updated for swift 3:
if you want to validate name and allow only letters for User Name then used below simple lines of code :
// function definition:
func isValidName(_ nameString: String) -> Bool {
var returnValue = true
let mobileRegEx = "[A-Za-z]{3}" // {3} -> at least 3 alphabet are compulsory.
do {
let regex = try NSRegularExpression(pattern: mobileRegEx)
let nsString = nameString as NSString
let results = regex.matches(in: nameString, range: NSRange(location: 0, length: nsString.length))
if results.count == 0
{
returnValue = false
}
} catch let error as NSError {
print("invalid regex: \(error.localizedDescription)")
returnValue = false
}
return returnValue
}
// function call :
var firstName = mEnterFirstNameTextField.text!
let isFirstNameValid = isValidName(firstName)
if isFirstNameValid{
// do user logic
}else{
// show error msg: -> "Enter name is not valid, please enter again..."
}