title: Why can't an ExtJS component call markInvalid() on itself?
body: <p>I have an 3.0.0 ExtJS web application in which I need to have an Ext.form.NumberField have a listener needs be able to mark the NumberField itself invalid.  </p>
  
  <p>Trouble is, this doesn't work when I try to call the markInvalid() function from within the listener function.  It works fine when I call it from anywhere else - but not from inside the listener of the number field itself.</p>
  
  <p>Here is the code...</p>
  
  <pre><code>var myNumberField = new Ext.form.NumberField({
  
      id: "myNumberField",
  
      listeners : {
          'render': function(c) {
  
  
              c.getEl().on('keyup', function() {
  
                  this.markInvalid("Marking this invalid!!");
              }, c);
  
           }
      },
  });
  </code></pre>
  
  <p>It's weird - the markInvalid works just fine if I set the component at any other place.  I can even set it fine from another component's listener - I just can't set it in the component itself.  It sort of flashes invalid for an instant, and then goes back.</p>
  
  <p>Please - I'm really at my wit's end with this.  Any help would be greatly appreciated!!</p>
  
  <p>Thanks in advance,
  Tim </p>