title: ignore hidden empty textboxes
body: <p>Quick update, i found out why the code wont work, all the textboxes i want to check are in groupboxes and thats the problem, if i remove the groupbox the problem is resolved. 
  Is there a way around this ?</p>
  
  <p>Found the solution.
  Posted below for future reference.</p>
  
  <p>Thanks again for all your imput.</p>
  
  <pre><code>        foreach (var textBox in Controls.OfType&lt;GroupBox&gt;().SelectMany(groupBox =&gt; groupBox.Controls.OfType&lt;TextBox&gt;()))
      {
          if (textBox is TextBox &amp;&amp; textBox.Visible &amp;&amp; string.IsNullOrEmpty(textBox.Text))
          {
              MessageBox.Show($"Missing {textBox.Name} value!");
              Focus();
              return;
          }
      }
  </code></pre>