如何使用setGridParam向jqgrid添加参数？

Question

此代码正常运行：

$("#list").jqGrid({
...
postData: { filters:'{"groupOp":"AND","rules":[{"field":"category_id","op":"eq","data":"mydata"}]}' },
search: true,
...
});

我尝试使用setGridParam方法添加这些参数：

jQuery("#list").setGridParam({
    postData: { filters:'{"groupOp":"AND","rules":[{"field":"category_id","op":"eq","data":"mydata"}]}' },
    search: true,
}).trigger('reloadGrid');

但它不起作用