title: ExtJs: grid.reconfigure Error "Uncaught TypeError: Cannot read property 'getProxy' of undefined"
body: <p>im trying to build an dynamic Grid is it possible to create an store from </p>
  
  <pre><code>var data = JSON.parse(response.responseText),
  columns = data.columns;
  var store = Ext.create('Ext.data.Store', {
      data: data
      })
  </code></pre>
  
  <p>cause i would like to reconfigure my grid which is displayed in window.js </p>
  
  <pre><code>grid.reconfigure({
          columns: columns,
          store : store
      });
  </code></pre>