title: ExtJS window dynamically add GridPanel items and show it
body: <p>I want to show only one GridPanel,which I dynamically add by switch click button event, in window.</p>
  
  <pre><code>var event_menu = new Ext.menu.Menu( {
      id : "event_menu",
      items : [ {
          text : 'record1',
          handler : function() {
              win.add(item_list_panel);//dynamica add GridPanel to show server data
              win.doLayout();
              item_list_store.load();
          }
      }, {
          text : 'record2',
          handler : function() {
                             win.remove(item_list_panel);//I want to remove it inorder to show the item_list_panel2 and only show one panel.
              win.add(item_list_panel2);
              win.doLayout();
              item_list_store.load();
          }
      } ]
  });
  </code></pre>
  
  <p>and this menu belong to my window tbar.
  when I click record win will show <code>item_list_panel</code> and I want to when I click <code>record2</code> the <code>item_list_panel2</code> will show in win and <code>item_list_panel</code> will hide.
  If I <code>win.remove(item_list_panel)</code> will have an error :</p>
  
  <pre><code>c.getPositionEl().dom is undefined
  </code></pre>
  
  <p>How can I do it,Thanks</p>