How to limit character for username in Swift - swift

Question

i need to limit character for username in my swift code.
Username only can use those characters "abcdefghijklmnopqrstuvwxyz._1234567890".
Please forgive me if i'm noob, i don't have programming background. Still learning .
Below are swift code, which part i need to edit ?
// MARK: - SIGNUP BUTTON
#IBAction func signupButt(_ sender: AnyObject) {
dismissKeyboard()
// You acepted the TOS
if tosAccepted {
if usernameTxt.text == "" || passwordTxt.text == "" || emailTxt.text == "" || fullnameTxt.text == "" {
simpleAlert("You must fill all fields to sign up on \(APP_NAME)")
self.hideHUD()
} else {
showHUD("Please wait...")
let userForSignUp = PFUser()
userForSignUp.username = usernameTxt.text!.lowercased()
userForSignUp.password = passwordTxt.text
userForSignUp.email = emailTxt.text
userForSignUp[USER_FULLNAME] = fullnameTxt.text
userForSignUp[USER_IS_REPORTED] = false
let hasBlocked = [String]()
userForSignUp[USER_HAS_BLOCKED] = hasBlocked
// Save Avatar
let imageData = avatarImg.image!.jpegData(compressionQuality: 1.0)
let imageFile = PFFile(name:"avatar.jpg", data:imageData!)
userForSignUp[USER_AVATAR] = imageFile
userForSignUp.signUpInBackground { (succeeded, error) -> Void in
if error == nil {
self.hideHUD()
let alert = UIAlertController(title: APP_NAME,
message: "We have sent you an email that contains a link - you must click this link to verify your email and go back here to login.",
preferredStyle: .alert)
// Logout and Go back to Login screen
let ok = UIAlertAction(title: "OK", style: .default, handler: { (action) -> Void in
PFUser.logOutInBackground(block: { (error) in
self.dismiss(animated: false, completion: nil)
})
})
alert.addAction(ok)
self.present(alert, animated: true, completion: nil)
// ERROR
} else {
self.simpleAlert("\(error!.localizedDescription)")
self.hideHUD()
}}
}

Answer 1

You can use regex for this, check out the code below.
let usernameRegex = "^[a-zA-Z0-9]{4,10}$"
let usernameTest = NSPredicate(format:"SELF MATCHES %#", usernameRegex)
print(usernameTest.evaluate(with: "asAZ")) // boolen
You can even create an extension out of it like this
extension String {
func isValidUserName() -> Bool{
let usernameRegex = "^[a-zA-Z0-9]{4,10}$" // your regex
let usernameTest = NSPredicate(format:"SELF MATCHES %#", usernameRegex)
return usernameTest.evaluate(with: self)
}
}
use it like this
yourText.isValidUserName() // return true or false .
You can google any kind of regex to fit your case, and future ones, i even recommend saving those regex in an enum, and create a function that accept those enums and validate, look at this as a hint
enum ValidationRgex: String {
case username = "^[a-zA-Z0-9]{4,10}$"
}
extension String {
func isValid(_ regex: ValidationRgex) -> Bool{
let usernameRegex = regex.rawValue
let usernameTest = NSPredicate(format:"SELF MATCHES %#", usernameRegex)
return usernameTest.evaluate(with: self)
}
}
"MyText".isValid(.username) // usage