title: Get other component value in a markup extension
body: <p>I started using markup extensions a few days ago and i got a dump problem.</p>
  
  <p>I have a markup extension that have <code>string</code> property and I wan't to use the value entered by the uer in a <code>TextBox</code>, is there an easy way to do that ?</p>
  
  <p>so i have something like that:</p>
  
  <pre><code>&lt;TextBox Name="tb"/&gt;
  
  &lt;ListView Name="lv"&gt;
      &lt;ListView.View&gt;
          &lt;GridView&gt;
              &lt;GridViewColumn Header="Value" DisplayMemberBinding="{Binding Path=Value, Converter={my:CustomExtension Value=(content of the textBox)}}" /&gt;
          &lt;/GridView&gt;
      &lt;/ListView.View&gt;
  &lt;/ListView&gt;
  </code></pre>