title: Get reference to itemId in Extjs
body: <p>I have a Window class like this:</p>
  
  <pre><code>Ext.define('EMS.tf.alerts.alerts.view.AlertWindow', {
      extend: 'Ext.window.Window',
      alias: 'widget.ems-alerts-window',
      height: 220,
      width: 600,
      alertTpl: undefined,
      autoScroll: true,
      selectedRecord: undefined,
      title: undefined,
      atext: undefined,
  
      // @private
      initComponent: function() {
          var me = this;
  
          Ext.apply(me, {
              tpl: me.alertTpl,
              listeners: {
              show: function() {
                  Ext.create('Ext.Container', {
                      renderTo: 'alertContainer',
                      itemId: 'buttonContainer',
                      items   : [{
                              xtype: 'button',
                              cls: 'ackbtn',
                              text : 'Acknowledge',
                              name: 'ackButton',
                              itemId: 'renderbutton'
                          },{
                              xtype: 'button',
                              cls: 'attchmntbtn',
                              text : 'Attachment',
                              name: 'attButton',
                              itemId: 'renderattachmntbutton'
                          }]
                      });
                  }
              },          
              title: me.title
          });
          me.callParent();
      }
  });
  </code></pre>
  
  <p>I want to get reference to button "Attachment" using itemId "renderattachmntbutton". How to do this?</p>
  
  <p>I tried windowobject.down('#renderattachmntbutton') but still it didn't work. I can get reference to the items placed before init function but not like this. Any idea on what needs to be done to get reference to this button?</p>