Count no of rows loaded on gridview

hello , i am working on form . i used two filters first one on comboBox and second one on the StringEdit lookup selection control . i used "select count (field) from Mydatasource " query on init method of form and show that count on StringTextCount label , total no of record are shown properly but when i select comboBox or Lookup then count is not working where i need to get total
number of loaded and filtered row count i used numberOfRowsLoaded() method on buttonclick but its not working , i am new and dont no how to properly state the problem so sorry for that already ....