title: Extjs4: how do I add a listener when I change my panel
body: <p>How do I add a listener when I change my panel to another panel in same tab?</p>
  
  <p>I know there is a function is tabchange, when my tab is changed and listener is working. </p>
  
  <p>Like this:</p>
  
  <pre><code>tabchange:function(tabPanel, tab){
     if(tab.id == "selecttraffic"){
        setclickmap = 'line';
        map.addControl(clickmap);
        clickmap.activate();
     } else if(tab.id == "selectrange"){
        setclickmap = 'range';
        map.addControl(clickmap);
        clickmap.activate();
     }
  }
  </code></pre>
  
  <p>But I can't find a similar function work to my panel change!!!</p>
  
  <p>Thanks! </p>