C# checking white space in a textbox

Question

How can I check in C# that is there a white space only in a textbox and perform some operation after that?

Answer 1

        var Rxwhitesp = new Regex(@"\s");

        string textboxstring = textbox.Text;
        string textboxfirststring = textbox.Text.First().ToString();
        if (Rxwhitesp.IsMatch(textboxfirststring) && (textboxstring.Length == 1))
        {
            // write code for true condition
        }
        else
        {
            // write code for false condition
        }