Format currency in textfield in Swift on input

Question

I am trying to format currency input in a textfield in Swift as the user inputs it.

So far, I can only format it successfully when the user finishes inputting:

Answer 1

I worked out a normal currency format ( eg 1 is as $1.00, 88885 is as $8,8885.00 and 7555.8569 as $7,555.86.

@IBAction func lostpropertyclicked(sender: AnyObject) {
    var currentString = ""
    currentString = amountTF.text
    formatCurrency(string: currentString)
}

func formatCurrency(#string: String) {
    println("format \(string)")
    let formatter = NSNumberFormatter()
    formatter.numberStyle = NSNumberFormatterStyle.CurrencyStyle
    formatter.locale = NSLocale(localeIdentifier: "en_US")
    var numberFromField = (NSString(string: currentString).doubleValue)
    currentString = formatter.stringFromNumber(numberFromField)!
    println(currentString )
}