Sqldatasource Return Null !

hi

 i am trying to get the output of the select statements of sqldatasource :

 protected void Page_Load(object sender, EventArgs e)

{

if (!IsPostBack)
        {
            DataView dv;
            dv = (DataView)(this.SqlDataSourcePictures.Select(DataSourceSelectArguments.Empty));
        }

}

the problem is that dv returns null ?

 and here is the sqldatasource definition in .aspx page

<asp:SqlDataSource ID="SqlDataSourcePictures" runat="server" ConnectionString="<%$ ConnectionString:con1%>"

SelectCommand="SELECT URL FROM SchoolPictures WHERE (School_Code = @School_Code) AND (SchoolPictureCategory = @SchoolPictureCategory)" OnSelecting="SqlDataSourcePictures_Selecting" OnSelected="SqlDataSourcePictures_Selected">

<SelectParameters>

<asp:QueryStringParameter Name="School_Code" QueryStringField="bid" Type="Int16" />

<asp:ControlParameter ControlID="ddlCat" Name="SchoolPictureCategory" PropertyName="SelectedValue"

Type="Int16" />

</SelectParameters>

</asp:SqlDataSource>

 

thanks for help