title: radio buttons in knockout
body: <p>I'm using knockout and I have 2 radio buttons, when a particular one is selected I need a textbox to be enabled and disabled if the other option is selected. I can't seem to get this working. this is what i have so far: IssercentageBased is a boolean on my viewmodel and i've set it up to be an observable. any ideas?</p>
  
  <pre><code>&lt;input type="radio" name="IsPercentageBased" value="true" data-bind="checked: IsPercentageBased"/&gt;
              &lt;span&gt;Percentage&lt;/span&gt;
              &lt;input type="radio" name="IsPercentageBased" value="false" data-bind="checked: IsPercentageBased"/&gt;
              &lt;span&gt;Value&lt;/span&gt;
  
   @Html.TextBox("Value", "", new
                  {
                      type = "text",
                      data_bind = "value: Value, valueUpdate: 'afterkeydown', disable: IsPercentageBased"
                  })
  </code></pre>