Sqldatasource control set dynamic Connectionstring in .aspx page only

Dynamically Set ConnectionString of SqlDataSource ASP.NET Control Inside GridView Template

Intro:
The SqlDataSource control enables you to use a Web server control to access data that is located in a relational database. You can use the SqlDataSource control with data-bound controls such as the GridView, FormView, and DetailsView controls to display and manipulate data on an ASP.NET Web page, using little or no code.

Here in this article i am writting how to set Dynamically ConnectionString Attribute on  SqlDataSource ASP.NET Control. Setting connection string for SqlDataSource control can de done programmatically in the code-behind ie (.aspx.cs) file.

On Page_Load:

SqlDataSource1.ConnectionString = yourconnectionstring;

If the SqlDataSource control is  inside the FooterTemplate of a GridView control then it will not be accessible at Page_Load. Here's the challenging task how to set ConnectionString on SqlDatasource control under Gridview Templates.
By following below steps you can achive this:
Step 1:
Here sample code of gridview templates:

<footertemplate>
<asp:dropdownlist autopostback="True" datasourceid="sqldsWorkcategory" datatextfield="name_wt" datavaluefield="id_wt" id="cmbfWorkCategory" onselectedindexchanged="cmbfWorkCategory_SelectedIndexChanged" runat="server" width="118">
</asp:dropdownlist>
<asp:sqldatasource connectionstring="&lt;%$ RepConnectionString: " getconnection="getconnection">"
id="sqldsWorkcategory" runat="server"
selectcommand="SELECT [id_wt], [name_wt] FROM [yourtablename]"&gt;
</asp:sqldatasource>
</footertemplate>

Step 2:
Now edit your web.config file
As i have many connection so have make a diifernt XML file to store all connections key

<configsource onstring.xml="onstring.xml" pp_data="pp_data">
<!-- Now Add this pieace of code under Compilation as u can see. -->
<compilation debug="true" targetFramework="4.0">
<expressionbuilders>
<add expressionprefix="RepConnectionString" type="RepConnectionStringExpressionBuilder">
</add></expressionbuilders>

</configsource>

Step 3:
Add class file inside App_code.
Have named as CodeExpressionBuilder.cs.
Note: using System.CodeDom; is needed
if u find error then add refference or google for this namespace,

Code of CodeExpressionBuilder.cs
just copy as it is.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.Compilation;
using System.Configuration;
using System.IO;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Data.SqlClient;
using System.Data;
using System.Collections.Generic;
using System.Xml.Linq;
using System.Xml;
using System.CodeDom;

//this is what we set in .aspx page (ie sqldatacource control)
[ExpressionPrefix("RepConnectionString")]
public class RepConnectionStringExpressionBuilder : ExpressionBuilder
{

public override CodeExpression GetCodeExpression(BoundPropertyEntry entry, object parsedData, ExpressionBuilderContext context)
{
 CodeTypeReferenceExpression thisType = new CodeTypeReferenceExpression(base.GetType());
 CodePrimitiveExpression expression = new CodePrimitiveExpression(entry.Expression.Trim().ToString());
 string evaluationMethod = "GetConnectionString"; //
 return new CodeMethodInvokeExpression(thisType, evaluationMethod, new CodeExpression[] { expression });
}
public static string GetConnectionString(string expression)
{
 string getcon1='Some thing lke ur connectionstring... form xml'
 SqlConnection conn = new SqlConnection(ConfigurationManager.ConnectionStrings[getcon1].ConnectionString);
 string wConnString = conn.ConnectionString;
 return wConnString;
}
}

This will set your dynamic ConnectionString for SqlDataCource control on .aspx page.
Debug n get the flow of code.Enjoy.......