title: Prevent extjs4's treegrid load data at the initialization
body: <p>I'm using the EXTJS4's tree grid (<code>Ext.tree.panel</code>).</p>
  
  <p>I have create a model and treestore to load the tree data, and specified the store to the treegrid, the code is the following:</p>
  
  <pre><code>var complist = Ext.create('Ext.data.TreeStore', {
      model: PFSComponent,
      proxy: {
          type: 'ajax',
          url: 'getpfscomponents.php',
          reader: {
              type: 'json'
          }
      }
  });
  
  var compPanel = Ext.create('Ext.tree.Panel', {
      title: 'lowdisks',
      height: 300,
      collapsible: false,
      useArrows: false,
      rootVisible: false,
      multiSelect: false,
      singleExpand: false,
      region: 'south',
      store: complist,
      columns: [{
          xtype: 'treecolumn', //this is so we know which column will show the tree
          text: 'name',
          flex: 2,
          sortable: false,
          dataIndex: 'name'
      }, {
          text: 'type',
          dataIndex: 'type',
          flex: 1,
          sortable: false
      }, {
          text: 'device',
          dataIndex: 'devicename',
          flex: 1,
          sortable: false
      }, {
          text: 'mount',
          dataIndex: 'mount',
          flex: 1,
          sortable: false
      }]
  });
  </code></pre>
  
  <p>When the page load, the <code>treegrid</code> will load the data auto, it works very good!</p>
  
  <p>But now I want to do something such as check the db, before the grid loaded. </p>
  
  <p>So I need implement the functions like the following :</p>
  
  <ol>
  <li>check whether the data is satisfied with the request</li>
  <li>if it's , the <code>treegrid</code> load the data</li>
  <li>or, alert the user</li>
  </ol>
  
  <p>So my question is how to prevent the <code>treegrid</code> to load the data when <code>initialization</code>?</p>
  
  <p>Thank you very much!</p>