TextBox txtb = new TextBox();
txtb.ID = "txt_P_" + i;
txtb.Text = "";
txtb.EnableViewState = true;
txtb.TextMode = TextBoxMode.MultiLine;
txtb.Width = Unit.Pixel(650);
txtb.Height = Unit.Pixel(400);
Panel1.Controls.Add(txtb);

foreach (Control txtb in Panel1.Controls)
        {
            if (txtb is TextBox)
            {                
                text+= ((TextBox)txtb).Text;
            }
        }

Page.FindControl("txt_P_1");

UpdatePanel.ContentTemplateContainer.Controls 

CollapsiblePanelExtender1.TargetControlID = Panel2.FindControl(Panel2.ID).ToString();
        CollapsiblePanelExtender1.ExpandControlID = Panel1.FindControl(Panel1.ID).ToString();
        CollapsiblePanelExtender1.CollapseControlID = Panel1.FindControl(Panel1.ID).ToString();
    }

$(window).bind('load', function() {
    var imgPoll = new Image();
    imgPoll.src = 'images/red-bar.png';
    $("#btnSubmit").mouseover(function() {
        $("#btnSubmit").css("background-color", "#6699cc")
    });
    $("#btnSubmit").mouseout(function() {
        $("#btnSubmit").css("background-color", "#336699")
    });

    if ($("#divVoted").length > 0) //Already voted
    {
        animateResults();
        $("#ctl00_RightContent_Headertxt").text("РЕЗУЛЬТАТЫ ОПРОСА");
    }

    else {

        $("#rdoPoll0").attr("checked", "checked"); //default select the first Choice
        $("#btnSubmit").click(function() {
            alert('ha-ha');
            $("#divPoll").css("cursor", "wait"); //show wait cursor inside Poll div while processing
            $("#btnSubmit").attr("disabled", "true") //disable the Vote button while processing

            var pID = $("input[id$=hidPollID]").val(); //get Poll ID
            var cID = $("input[name='rdoPoll']:checked").val(); //get the checked Choice
            var data = "{'pID':'" + pID + "', 'cID':'" + cID + "'}"; //create the JSON data to send to server
            alert(data);
            $(document).ajaxSend(function() { alert("ajax send") });
            $(document).ajaxError(function() { alert("ajax error") });
            $(document).ajaxComplete(function() { alert("ajax Complete") });
            $.ajax(
                { //call the Page method using JQuery ajax
                    beforeSend: function() { alert("beforeSend") },
                    type: "POST",
                    url: "Test.aspx/UpdatePollCount",
                    data: data,
                    contentType: "application/json; charset=utf-8",
                    dataType: "json",
                    timeout: 10000,
                    success: function(msg)  //show the result
                    {
                        alert(msg.d);
                        $("#ctl00_RightContent_Headertxt").text("РЕЗУЛЬТАТЫ ОПРОСА");
                        $("#divPoll").css("cursor", "default"); //remove the wait cursor
                        $("#btnSubmit").attr("disabled", "false") //enable the Vote button

                        $("div[id$=divAnswers]").fadeOut("fast").html(msg.d).fadeIn("fast", function() { animateResults(); });
                    },
                    error: function() { alert(msg.d); alert("error") }
                });
        });
    }

    function animateResults() {
        $("div[id$=divAnswers] img").each(function() {
            var percentage = $(this).attr("val");
            $(this).css({ width: "0%" }).animate({ width: percentage }, 'slow');
        });
    }
});

[WebMethod]
    public static string UpdatePollCount(int pID, int cID)
    {
        //int pollID = pID;
        //int choiceID = cID;
        //update the vote count of the selected choice
        Poll objPoll = new Poll();
        objPoll.UpdateChoiceVote(cID);

        //save the users IP address - to block repeated vote if the BlockMode is by IP address
        string ip = HttpContext.Current.Request.ServerVariables["REMOTE_ADDR"];
        objPoll.InsertPollIP(pID, ip);

        //Save the poll ID in cookie - to block repeated vote if the BlockMode is by Cookie
        HttpCookie pollCookie;// = new HttpCookie("Poll");
        string valueToStore = ""; //we store the poll IDs as comma seperated values

        //the cookie already exists and some PollIDs are already there
        if (HttpContext.Current.Request.Cookies["Poll"] != null && HttpContext.Current.Request.Cookies["Poll"]["ID"] != null)
        {
            pollCookie = HttpContext.Current.Request.Cookies["Poll"];
            valueToStore = HttpContext.Current.Request.Cookies["Poll"]["ID"] + "," + pID.ToString(); //append the current PollID to the already existing Poll IDs after a comma
        }
        else //cookie not exists - create a new one and store the ID
        {
            pollCookie = new HttpCookie("Poll");
            valueToStore = pID.ToString();
        }
        pollCookie.Values["ID"] = valueToStore;
        pollCookie.Expires = DateTime.MaxValue; //this cookie will never expire
        HttpContext.Current.Response.Cookies.Add(pollCookie);

        //get the poll result
        DataSet dsPoll = objPoll.SelectPoll(pID);
        bool blockBtn = false;
        string temp = HttpContext.Current.Request.Cookies["BlockBtn"].Value;
        return temp == "true" ? getResultHTML(dsPoll, true) : getResultHTML(dsPoll, false);
    }

string sUserName = Page.User.Identity.Name;

WindowsPrincipal wpMain = new WindowsPrincipal(WindowsIdentity.GetCurrent());
string sUserName = wpMain.Identity.Name;

<authentication mode="Windows"></authentication>

......
Button b = new Button();
b.Click += delegate(object sender1, EventArgs e1)
{
    b.Text = "newCaption";
};
......

IsPostBack
{
   код
}

<asp:LinkButton ID="LinkButton1" runat="server" OnClientClick="window.close()">Close</asp:LinkButton>

 DataSet ds = new DataSet();
            da.Fill(ds, "testtable");
            DataTable table = ds.Tables[0];
            DataRow row = table.Rows[0];
            row["test"] = "test123test";

        <uc1:WebUserControl1 ID="WebUserControl1" runat="server" >
            <uc2:WebUserControl2 ID="WebUserControl2" runat="server" >
            </uc2:WebUserControl2>
            <uc2:WebUserControl2 ID="WebUserControl3" runat="server" >
            </uc2:WebUserControl2>
        </uc1:WebUserControl1>

        <uc1:WebUserControl1 ID="WebUserControl1" runat="server" >
            test text
        </uc1:WebUserControl1>