Hi santosh86,
I have cross checked the code and its working fine i am able to access the Tab Container in ASCX Page.
Refer below sample code and modify the code according to your need.
Master.master
<%@ Master Language="C#" AutoEventWireup="true" CodeFile="MasterPage.master.cs" Inherits="MasterPage" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
<title></title>
<asp:ContentPlaceHolder ID="head" runat="server">
</asp:ContentPlaceHolder>
</head>
<body>
<form id="form1" runat="server">
<div>
<asp:ContentPlaceHolder ID="ContentPlaceHolder1" runat="server">
</asp:ContentPlaceHolder>
</div>
</form>
</body>
</html>
GeneratePackage.aspx
<%@ Page Language="C#" AutoEventWireup="true" MasterPageFile="~/MasterPage.master"
CodeFile="GeneratePackage.aspx.cs" Inherits="_Default" %>
<%@ Register TagPrefix="ajx" Namespace="AjaxControlToolkit" Assembly="AjaxControlToolkit" %>
<%@ Register TagPrefix="cmp" TagName="Button" Src="~/ControlCompanyMaster.ascx" %>
<asp:Content runat="server" ContentPlaceHolderID="ContentPlaceHolder1">
<ajx:ToolkitScriptManager ID="ToolkitScriptManager1" runat="server">
</ajx:ToolkitScriptManager>
<ajx:TabContainer ID="tbcontainer" runat="server" ActiveTabIndex="0" Width="100%"
CssClass="fancy fancy-green" AutoPostBack="true">
</ajx:TabContainer>
<cmp:Button ID="Button1" runat="server" />
</asp:Content>
ControlCompanyMaster.ascx
<%@ Control Language="C#" AutoEventWireup="true" CodeFile="ControlCompanyMaster.ascx.cs"
Inherits="ControlCompanyMaster" %>
<%@ Register TagPrefix="ajx" Namespace="AjaxControlToolkit" Assembly="AjaxControlToolkit" %>
<asp:Button ID="btnSave" runat="server" Text="Submit" ValidationGroup="save" OnClick="btnSave_Click"
CssClass="btn" Style="float: left; margin-left: 500px; margin-top: 5px;" />
ControlCompanyMaster.ascx.cs
protected void btnSave_Click(object sender, EventArgs e)
{
AjaxControlToolkit.TabContainer tbcontainer = this.Parent.FindControl("tbcontainer") as AjaxControlToolkit.TabContainer;
}
ScreenShot
