DropDownList Not refreshing .refresh() is undefined ??

[Chanaka]

Code:
$("#DropDownList1").change(function () {
   custCode = $("#DropDownList1").val();

   $("#titles").data("kendoDropDownList").dataSource.read(); //shows list Loading But Same Data Is present .
   $("#titles").data("kendoDropDownList").refresh(); //NOT Working 

});

I am Tring to refresh my DropDownList after another DropDownList ..
is clicked but the refresh Method is not define error pops.
therefor i use the dataSource.read() then the DropDownList Shows it loading but data remain the
same