title: How to detect real value change in GXT Combobox
body: <p>I'm new to Ext GWT and working with GXT (2.2.5). I want to add an alert when a combo-box changes its value. But the change event fire when re-select the same item. This is part of my code:</p>
  
  <pre><code>    @override
      public void handleEvent(BaseEvent be) {
          if (be.getType() == Events.Change) {
              //add alert
          }
      }
  </code></pre>
  
  <p>I wonder how to get the REAL value change event. And if it doesn't exist, how can I get the previous value from the combo-box.</p>