Formatting a UITextField for credit card input like (xxxx xxxx xxxx xxxx)

Question

I want to format a UITextField for entering a credit card number into such that it only allows digits to be entered and automatically inserts spaces so that the

Answer 1

Yet another version of the accepted answer in Swift 2...

Ensure you have these in your delegate instance:

private var previousTextFieldContent: String?
private var previousSelection: UITextRange?

And also ensure that your text field calls reformatAsCardNumber:

textField.addTarget(self, action: #selector(reformatAsCardNumber(_:)), forControlEvents: .EditingChanged)

You text field delegate will need to do this:

func textField(textField: UITextField, shouldChangeCharactersInRange range: NSRange, replacementString string: String) -> Bool {
    previousTextFieldContent = textField.text;
    previousSelection = textField.selectedTextRange;
    return true
}

Lastly include the following methods:

func reformatAsCardNumber(textField: UITextField) {
    var targetCursorPosition = 0
    if let startPosition = textField.selectedTextRange?.start {
        targetCursorPosition = textField.offsetFromPosition(textField.beginningOfDocument, toPosition: startPosition)
    }

    var cardNumberWithoutSpaces = ""
    if let text = textField.text {
        cardNumberWithoutSpaces = self.removeNonDigits(text, andPreserveCursorPosition: &targetCursorPosition)
    }

    if cardNumberWithoutSpaces.characters.count > 19 {
        textField.text = previousTextFieldContent
        textField.selectedTextRange = previousSelection
        return
    }

    let cardNumberWithSpaces = self.insertSpacesEveryFourDigitsIntoString(cardNumberWithoutSpaces, andPreserveCursorPosition: &targetCursorPosition)
    textField.text = cardNumberWithSpaces

    if let targetPosition = textField.positionFromPosition(textField.beginningOfDocument, offset: targetCursorPosition) {
        textField.selectedTextRange = textField.textRangeFromPosition(targetPosition, toPosition: targetPosition)
    }
}

func removeNonDigits(string: String, inout andPreserveCursorPosition cursorPosition: Int) -> String {
    var digitsOnlyString = ""
    let originalCursorPosition = cursorPosition

    for i in 0.stride(to: string.characters.count, by: 1) {
        let characterToAdd = string[string.startIndex.advancedBy(i)]
        if characterToAdd >= "0" && characterToAdd <= "9" {
            digitsOnlyString.append(characterToAdd)
        }
        else if i < originalCursorPosition {
            cursorPosition -= 1
        }
    }

    return digitsOnlyString
}

func insertSpacesEveryFourDigitsIntoString(string: String, inout andPreserveCursorPosition cursorPosition: Int) -> String {
    var stringWithAddedSpaces = ""
    let cursorPositionInSpacelessString = cursorPosition

    for i in 0.stride(to: string.characters.count, by: 1) {
        if i > 0 && (i % 4) == 0 {
            stringWithAddedSpaces.appendContentsOf(" ")
            if i < cursorPositionInSpacelessString {
                cursorPosition += 1
            }
        }
        let characterToAdd = string[string.startIndex.advancedBy(i)]
        stringWithAddedSpaces.append(characterToAdd)
    }

    return stringWithAddedSpaces
}