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

Since you're explicitly asking for Swift, I've translated the top asnwer in the linked question.

let notAllowedCharacters = " ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789_.";

func textField(
    textField: UITextField,
    shouldChangeCharactersInRange range: NSRange,
    replacementString string: String)
    -> Bool
{
    let set = NSCharacterSet(charactersInString: notAllowedCharacters);
    let inverted = set.invertedSet;

    let filtered = string
        .componentsSeparatedByCharactersInSet(inverted)
        .joinWithSeparator("");
    return filtered != string;

}

Answer 2

Swift : 3 and a different approach:

Add a target function for the text field change in your viewDidLoad:

    override func viewDidLoad() {
    super.viewDidLoad()
textField.addTarget(self, action: #selector(ViewController.textFieldDidChange(textField:)), for: UIControlEvents.editingChanged)
 }

in the target function, simply detect the entered char and replace it with blank. I have tested it and it prevents the user from entering any non desirable characters in the text field.

 func textFieldDidChange(textField: UITextField) {

    if let textInField = textField.text{
        if let lastChar = textInField.characters.last{

            //here include more characters which you don't want user to put in the text field
            if(lastChar == "*")
            {

                textField.text  = textInField.substring(to: textInField.index(before: textInField.endIndex))

            }
        }
    }

}

Answer 3

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)
}

Although I read in an earlier post that CharacterSets do not support characters that are composed of more than one Unicode.Scalar; so use with caution I guess.

Answer 4

internal func textField(textField: UITextField, shouldChangeCharactersInRange range: NSRange, replacementString string: String) -> Bool{
     if let text = string{
           if text == "#" || text == "$" || text == "!"{ \\and so on
              return false
           }
     }
     return true
}

Answer 5

So this is probably the most robust way to restrict Spaces. Using this user won't be able to Paste/Type Whitespaces

This is how you can Implement using Swift 3.

Add below mentioned extension snippet to a Swift file;

extension String {

var containsWhitespace: Bool {
    for scalar in unicodeScalars {
        switch scalar.value {
        case 0x20:
            return true
        default:
            continue
        }
    }
    return false
  }
}

In your ViewController Swift file drag out your Editing Changed Instance and a Referencing Outlet of UITextField from Storyboard, the one mentioned in picture below:

Use the dragged Instances as mentioned below:

Referencing Outlet as:

@IBOutlet weak var textField: UITextField!

and Editing Changed as:

 @IBAction func textChanged(_ sender: UITextField) {
    if (textField.text!.containsWhitespace) == true {
        print("Restrict/Delete Whitespace")
        emailField.deleteBackward()
    } else {
        print("If Its not Whitespace, Its allowed.")
    }
}

This will detect and remove whitespace as soon as user tries to type/paste it.

Answer 6

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)
}