title: Allow only numbers and negative values
body: <p>I have a <code>textbox</code> which needs only accept numbers (can be decimal values) and negative values.</p>
  
  <p>Currently I have something like this in <code>KeyPress</code> event</p>
  
  <pre><code>   if (!char.IsControl(e.KeyChar) &amp;&amp; !char.IsDigit(e.KeyChar) &amp;&amp; e.KeyChar != '.')
      {
          e.Handled = true;                
      }
  </code></pre>
  
  <p>What else I should do in order to allow negative values?</p>
  
  <p>Thanks</p>