func changeText(_ range: NSRange, replacementText text: NSString) {
        if validInputStarted {
            if stringRange.location >= range.location && stringRange.location < range.location + range.length {
                validInputStarted = false
            } else if range.location < stringRange.location {
                stringRange.location -= range.length - text.length
            } else if range.location > stringRange.location && range.location <= stringRange.location + stringRange.length {
                stringRange.length -= stringRange.length - (range.location - stringRange.location) - text.length
            }

            var str = "";
            if stringRange.location + 1 < (textView.text as NSString).length {
                str = (textView.text! as NSString).substring(with: NSRange(location: stringRange.location + 1, length: stringRange.length - 1))
            }
        }
        if text.length > 0 && (text as NSString).substring(to: 1) == "@" {
            validInputStarted = true
            stringRange.location = range.location
            stringRange.length = text.length
        }
    }