title: combobox's Value is not load in extjs MVC
body: <p>I am working with ExtJS MVC and implementing Scheduler.</p>
  
  <p>I want to load my Store in my combo box but it was not load successfully.</p>
  
  <p><strong>My Store is</strong></p>
  
  <pre><code>Ext.define('gantt.store.serviceStore', {
      extend: 'Ext.data.Store',
      model: 'gantt.model.Service',
      storeId: 'serviceStore',
      autoLoad: true,
      autoSync: true,
      proxy: {
          type: 'ajax',
          api: {
              read: 'Event/Get'
          },
          reader: {
              type: 'json',
              root: 'data'
          },
          writer: {
              type: 'json',
              encode: true,
              writeAllFields: true,
              root: 'data'
          }
      }
  });
  </code></pre>
  
  <p><strong>My Model is</strong></p>
  
  <pre><code>Ext.define('gantt.model.Service', {
      extend: 'Sch.model.Event',
      fields: [{ name: 'ServiceId' },
          { name: 'ServiceName' },
          { name: 'Description' },
          { name: 'Rate' }
          ],
      proxy: {
          type: 'ajax',
          api: {
              read: 'Service/Get'
          },
          reader: {
              type: 'json',
              root: 'data'
          },
          writer: {
              root: 'data',
              type: 'json',
              encode: true,
              writeAllFields: true
          }
      }
  });
  </code></pre>
  
  <p>and My ComboBox Code is below..</p>
  
  <pre><code>this.combo = new Ext.form.ComboBox({
     id: 'statesCombo',
     store: 'serviceStore',
     displayField: 'ServiceName',
     valueField: 'ServiceName',
     hiddenName: 'ServiceId',
     typeAhead: true,
     mode: 'local',
     fieldLabel: 'Services',
     anchor: '100%',
     forceSelection: true,
     triggerAction: 'all',
     emptyText: 'Select a Service',
     selectOnFocus: true   })
  </code></pre>
  
  <p>My Problem is when I am Click on combo box my value is not loaded..
  and didnt display any Error.</p>