title: In an ExtJS Grid's actioncolumn, how do I make use of the `v` parameter that's passed to getClass/getTip?
body: <p>In an ExtJS grid, I have an <code>actioncolumn</code> that I want to have a different icon/tooltip based on the data in the row (actually, within a particular column of the row).</p>
  
  <p>The first parameter to the <code>getClass</code> and <code>getTip</code> callbacks is <code>v</code>, described in the documentation as:</p>
  
  <blockquote>
    <p>The value of the column's configured field (if any).</p>
  </blockquote>
  
  <p>I have defined my <code>actioncolumn</code> as follows, specifying the 'configured field' using the <code>dataIndex</code> property:</p>
  
  <pre><code>    {
          xtype: "actioncolumn",
          flex: 0.25,
          dataIndex: "action_name",  // Defines which field should be passed in as v, below
          getClass: function(v, metadata, r, rowIndex, colIndex, store) {
              // v is "", yet r.get("action_name") is "Capture Fill"
          }
      });
  </code></pre>
  
  <p>Within the <code>getClass</code> callback, I'm able to access the value of the *action_name* field through <code>r.get("action_name")</code>, but v is <code>""</code>.</p>
  
  <p>What am I doing wrong here?</p>