title: EXTJS - chart refresh, redraw - How to update a chart
body: <p>So I have a chart inside a panel. The panel contains two tabs. The first tab contains the chart. The second tab contains a small form that I am using to filter the data in the chart. </p>
  
  <p>My filtering form is pretty simple: it contains different time periods such as '7 days', '30 days', etc, and once selected, it sends the user selection (using ajax) to where I am generating the data for my chart. </p>
  
  <p>That's great and all... but how do I get the chart to UPDATE?! The user can select whatever option they want (and I know that the script is getting the data and changing the query), but the chart never changes. I think I'm supposed to use redraw or refresh.</p>
  
  <p>Here's what I'm thinking:  Add the redraw/refresh to my form handler here, looking something like this</p>
  
  <pre><code>        xtype: 'radiofield',
          name: 'timespan',
          id: 'radio3',
          inputValue: 30,
          boxLabel: '30 days',
          handler: function(checkbox, checked) {
             if (checked ) {
                console.log(checkbox.inputValue);
                **HERE**
              }
          }
  </code></pre>
  
  <p>Question: <strong>How can I update an EXTJS chart on a user action?</strong></p>