How to filter lookup values on a dialogfield in Report Dialog based on another dialogfield in AX 2012 AOT reports?

How can i implement Customized lookup in Report Dialog box.

for example i have two fields in my report dialog 1) Custgroup 2) CustAccount

if i have selected a particuler cust group in first field then second field lookup should show only customers those come under this cust groups.

My code is::::

//class

    public class ReportRun extends ObjectRun
    {

        DialogField dialogcustGroup,dialogcustaccount ;
        CustTable  obj_CustTable ;
    }

   //dialog method
   public Object dialog(Object _dialog)
{
    DialogRunbase dialog = _dialog;
    DialogGroup     toFromGroup;
    Args _args;
    str accountnum,custGroup;
    ;
   // _args =  new Args();
   //  obj_dev_CustTable = _args.record(); 
    //accountnum = obj_dev_CustTable.AccountNum;

    dialogcustGroup = dialog.addFieldValue(extendedTypeStr(CustGroup),CustGroup,"");

    while select obj_CustTable
         where obj_CustTable.AccountNum == dialogcustGroup .value()
    {
         CID     =  obj_dev_CustTable.CID;
     dialogcustaccount =dialog.addFieldValue(ExtendedTypeStr(AccountNum),accountnum,"CID");
    }


    return dialog;
}  

Any help would be great!!!!