title: Adding a listener to create a warning message to a textfield
body: <p>I have a combo box and a textfield. I am trying to Add a warning notifcation to the textfield stating 'please enter value' if something is selected from the combo box. However, I only want the warning to display on the textfield if '3' is selected from the combo box </p>
  
  <p>Is there any way that I could do that? I am not sure how to do that.</p>
  
  <p>Here is the code for my combobox and textfield:</p>
  
  <pre><code>{
                              xtype:'combo',
                              store: ['1','2','3'],
                              triggerAction: 'all',
                              fieldLabel: 'Area',
                              id: 'dcArea',
                              width: 125,
                          },{
                              xtype:'textfield',
                              fieldLabel: 'Mile',
                              id: 'mile',
                              width: 125,
                          }
  </code></pre>