Drop Down List Grid

[snjy85]

I am using SmartGwt 2.2, Browser Mozilla on windows xp.
Now issue I am facing is this :
I am using Drop Down List Grid.In this I want to filtering depends on some criteria.But I am not getting grid instance in which I can apply criteria & fetchData so U did as below which is not working :

					Criterion criterion=new Criterion();
					
					Criteria criteria = new Criteria();
					
					if (true) {
						criteria.addCriteria("isPreset", "false");
					}else 
					{
						criteria.addCriteria("isPreset", "true");
					}
					tableNames.setCriterion(criterion);
					tableNames.fetchData();

There is a field named as "isPreset" in the Drop Down Grid. But this is not working.When I saw examples of grid there is a method
grid.setFetchData(criteria);
But in case of ComboBox there is method combo.setFetchData().
So My question is that is it possible to get instance of grid which will render in combo box so that I can apply search criteria on it??
Or is there ant other way to filter data of Combo Box ???
Please help :(