title: EXTJS 4 : how to get combobox value with out determine combobox id
body: <pre><code>var StaticComboBox = Ext.define('MyApp.view.ComboBoxType', {
    extend: 'Ext.form.ComboBox',
    mode: 'local',
    fieldLabel: 'Type',
    labelWidth: 50,
    triggerAction: 'all',
    editable: false,
    valueField: 'value',
    displayField: 'label', 
    data: [
                 {value: 0, label: 'By Vehicle'},  {value: 1, label: 'By Route'}
            ] ,
    initComponent: function() {
      this.store = new Ext.data.Store({
        fields: ['value', 'label'],
        data: this.data
      });
      StaticComboBox.superclass.initComponent.call(this);
    },
    listeners: {
          change: function (combo, value) {
          var grid = Ext.ComponentQuery.query('dailywindow gridpanel[name=mydailychartgrid]')[0];
          if (grid != null){
              if (value == 0) {
              //grid.reconfigure(VehicleStore_Chart,VehicleModel)
              grid.reconfigure(VehicleStore_Chart);
              grid.columns[1].setText('Plat No');
              grid.columns[1].dataIndex = "Plat_No"
              grid.columns[1].width = 100
              }else{
  
              //grid.reconfigure(RouteNameStore_DailyChart,RouteModel)
              grid.reconfigure(RouteNameStore_DailyChart)
              grid.columns[1].setText('Route Code');
              grid.columns[1].dataIndex = "Route_Code"
              grid.columns[1].width = 100
              }
          }
          //alert(value);
          }
    }
  
  });
  
  var c = new StaticComboBox();
  c.setValue(0);
  </code></pre>
  
  <p>how do i get the combobox value without using determine id in combobox ?<br>
  <code>Ext.getCmp("ComboBoxType").getValue()</code> does not work.</p>