ios – Having issue to get the textField Type

When I type email address in email textfield, it goto the default case every time that’s why I am not allowed to enter “@” symbol.

  func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Bool {
        if textField.isValidInput(text: string, field: textField) {
            return true
        } else {
            return false
        }
    }


extension UITextField {
    func isValidInput(text: String, field: UITextField) -> Bool {
        
        let englishAndDigitsRegEx: String
        
        switch field.textContentType {
        case UITextContentType.emailAddress:
            englishAndDigitsRegEx = "^[a-zA-Z0-9@.]*$"
        case UITextContentType.password:
            return true
        default:
            englishAndDigitsRegEx = "^[a-zA-Z0-9]*$"
        }
        
        let englishAndDigitsTest = NSPredicate(format:"SELF MATCHES %@", englishAndDigitsRegEx)
        return englishAndDigitsTest.evaluate(with: text)
    }
}

I am expecting that make modular code that could be access from any view controller field to validate input according their textfield using regular expression.