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

Adding on to what @Evdzhan Mustafa said. You want to add a return statement in case the string is empty. Without it you won't be able to delete your text. Modified Code Below:

Swift 3 Version

let notAllowedCharacters = " ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789_.";

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

    print("String: \(string)")
    let set = NSCharacterSet(charactersIn: notAllowedCharacters);
    let inverted = set.inverted;

    let filtered = string.components(separatedBy: inverted).joined(separator: "")
    print("String Filtered: \(filtered)")
    return filtered != string;
}