弹出消息框

 ClientScript.RegisterStartupScript(this.GetType(), "aa", "alert('请输入必要信息');", true);
                //ScriptManager.RegisterStartupScript(this.UpdatePanel1, this.GetType(), "UpdatePanel2", "alert('请输入必要信息')", true);
                //Response.Write("<script>alert('请输入必要信息');</script>");
                //this.lblMsg.Text = "请输入必要信息";
                //Page.RegisterClientScriptBlock("","<script>alert('请输入必要信息!')</script>");