title: Extjs - Set focus field in panel
body: <p>I define a panel extend Ext.form.Panel with alias is: "example".
  <br>and in my viewport i init xtype = 'example' for my east.
  <br>I want when i collapse that panel (example) then my first field (datefield) will focus
  <br>I try some below code but not working</p>
  
  <pre><code>//1. not working
  ,listeners: {
       afterrender: function(field) {
           field.focus(true, 100);
       }
  }
  //2. not working
  Ext.getCmp('myDatefieldId').focus(true, 20);
  </code></pre>
  
  <p>How can i do that thanks</p>