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

This ensures multiple spaces are caught in your check.

 bool hasAllWhitespace = txtBox1.Text.Length>0 &&
                         txtBox1.Text.Trim().Length==0;

To check for a single space only:

 bool hasSingleWhitespace = txtBox1.Text == " ";