脚本管理器没有调用HttpContext

当我使用

ScriptManager.RegisterStartupScript(this.Page, Page.GetType(), "TTTT111", "alert('calling dfdfd from server .....');", true);

在

之前或之后

HttpContext.Current.Response.Clear();
HttpContext.Current.Response.ContentType = strContentType;
HttpContext.Current.Response.AddHeader("Content-Disposition", string.Format("attachment; filename={0}", strFileName));
HttpContext.Current.Response.OutputStream.Write(ExportDataString, 0, ExportDataString.Length);
HttpContext.Current.ApplicationInstance.CompleteRequest();
HttpContext.Current.Response.OutputStream.Flush();

则不调用scriptmanager