title: Argument exception with Text Box
body: <p>I have a text box. When I drag a file into it and click a button the file from text box is moved to another folder. But if I forget to drag a file to the text box and click a button, the program throws an Argument Exception that sourceFileName isnt't present.</p>
  
  <pre><code>private void button_Click(object sender, EventArgs e)
  {
      // here occurs Argument Exception Because there isn't any TextBox.Text
      File.Copy(TextBox.Text, "C:/");
  
      if (String.IsNullOrEmpty(TextBox.Text))
          {
              MessageBox.Show("Please drag a file to the Tex Box!");
          }
  }
  </code></pre>
  
  <p>How can I catch that Argument Exception of a missing Source File?</p>