NSTextField with only numbers and size limitation

onlyNumberAndTextFieldSizeLimitation.swift

extension MainViewController: NSTextFieldDelegate {
    
    func controlTextDidChange(_ obj: Notification) {

        let textField = obj.object as! NSTextField
        
        let charSet = NSCharacterSet(charactersIn: "1234567890").inverted

        textField.onlyNumberAndTextFieldSizeLimitation(charset: charSet)
   
    
}

extension NSTextField {
    
    func onlyNumberAndTextFieldSizeLimitation(charset: CharacterSet) {
        
        let chars = stringValue.components(separatedBy: charset)
        stringValue = chars.joined()
        
        if stringValue.count > 8 {
            stringValue = String(stringValue.dropLast())
        }
        
    }
    
}