Forms Data Controls :: GridView Can't Filter Because Of Object Data Source?

I have the web page that meet the problem. There exists a gridview and filtering. When Select all by using function A, it is OK. when Filter by using function B, it cannot filter and return no rows. When Select all again, it is OK. I have tested that function B can return the corrected filtered rows. But when databind in the web page, it cannot show and no error?

<ContentTemplate>
<asp:GridView ID="gvwBOM" runat="server" DataKeyNames="ProductID"
AutoGenerateColumns="False" DataSourceID="objBOM" AllowPaging="True"
AllowSorting="True" BorderWidth="0px" CellPadding="3" CellSpacing="1" CssClass="grid-view"
OnRowCreated="gvwBOM_RowCreated"
OnRowCommand="gvwBOM_RowCommand"
OnDataBound="gvwBOM_DataBound" >
.........
<asp:ObjectDataSource ID="objBOM" runat="server"
SelectMethod="GetALTBOMs"
SelectCountMethod="GetALTBOMsCount"
EnablePaging="true"
SortParameterName="SortExpression"
TypeName="QI.BLL.WMS.ALTBOM" >
private void FillGridView(string filter)
{
if(filter == "0")
{
objDataSourceSelect="Afunction";
this.objBOM.SelectParameters.Clear();
}
else
{
objDataSourceSelect="Bfunction";
this.objBOM.SelectParameters.Clear();
this.objBOM.SelectParameters.Add("productSupplimentID", ddlTmp.SelectedValue);
}
this.objBOM.SelectMethod = objDataSourceSelect;
this.objBOM.SelectCountMethod = objDataSourceSelect + "Count";
this.gvwBOM.DataBind();
}