问组合框中的默认值作为存储中的值

EN

  var fields = {
  fields: ['text'] 
};
var notfields ={
  fields:['category']
}
this.store = new GO.data.JsonStore({
  url: GO.settings.modules.infoscherm.url + 'json.php',
  baseParams:{
    task:'selects'
  },
  root: 'results',
  fields: fields.fields
});

  this.selectedCat = new GO.data.JsonStore({
  url: GO.settings.modules.infoscherm.url + 'json.php',
  baseParams: {
    task:'currentselectedcat',
    id:'id'
  },
  root: 'results',
  fields: notfields.fields
});


  this.category = new Ext.form.ComboBox({
  name: 'category', 
  width: 100,
  store: this.store, 
  fieldLabel: "Categorie", 
  displayField:'text', 
  triggerAction: 'all', 
  editable: false, 
  selectOnFocus:true, 
  value: this.selectedCat //returns [object Object] naturally
});