How to restrict certain characters in UITextField in Swift?

Question

I am creating a trivia application that asks for a username on start up. I\'d like to make it impossible to use characters such as #$@!^& etc (also including \"space\").

Answer 1

Swift 4 iOS 11.2.x based on using an extension, tests to see if a string is a valid hex number in this example.

extension String {

var containsValidCharacter: Bool {
    guard self != "" else { return true }
    let hexSet = CharacterSet(charactersIn: "1234567890ABCDEFabcdef")
    let newSet = CharacterSet(charactersIn: self)
    return hexSet.isSuperset(of: newSet)
  }
}

You use it like with the UITextFieldDelegate.

func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Bool {
    return (string.containsValidCharacter)
}