如何基于过滤器选项重新加载JQGrid？

I have a JQgrid, By default this will display all data's(say All, xxx, yyy, zzz). I have a filter drop-down, by default with "All" selected. If I change to xxx, it should call a function by passing "xxx" to call a struts action. Based on the action's return value (JSON data) the jqgrid should populate again with the new data. As of now, It is calling "All" even I select "xxx". How to achieve this? I have a JQgrid, By default this will display a