Client Side Callbacks in ASP.NET 2.0

ASP.NET 2.0 includes a new Client Callback feature that enables you to retrieve page values and populate them to an already-generated page with out reconstructing page. This makes it possible to use on a page with out going through the entire post back cycle; that means you can update your pages without completely redrawing the page.
So you can do partial postback like ajax without using the update pannel of Ajax.
In my following example I am taking two dropdown list,on change the value of first dropdown it will populate the values of second dropdown without any postback.

Step 1. First take two dropdownlist in the body of your HTML
<asp:DropDownList ID="DropDownList1" AutoPostBack="false" runat="server" >
<asp:ListItem>A</asp:ListItem>
<asp:ListItem>B</asp:ListItem>
<asp:ListItem>C</asp:ListItem>
</asp:DropDownList>
<asp:DropDownList ID="DropDownList2" runat="server">
</asp:DropDownList></div>

Step 2.Declare a class level variable (before the pageload event and within the class)
private string earg;

Step 3.Inherit The Interface ICallbackEventHandler as follows
public partial class Default2 : System.Web.UI.Page, ICallbackEventHandler

Step 4. Now Implement the interface ICallbackEventHandler

#region ICallbackEventHandler Members

public string GetCallbackResult()
{
System.Text.StringBuilder sb1 = new System.Text.StringBuilder();
string strDropDownList1Value = this.earg;

DataSet ds = getDropDownList2Values(strDropDownList1Value);

for (int i = 0; i < ds.Tables[0].Rows.Count; i++)
{
sb1.Append(ds.Tables[0].Rows[i][0]);
sb1.Append("");
sb1.Append(ds.Tables[0].Rows[i][1]);
sb1.Append("");
}
return sb1.ToString();
}

public void RaiseCallbackEvent(string eventArgument)
{
this.earg = eventArgument;
}

#endregion

Step5.Write a function that will populate the value of second dropdown
protected DataSet getDropDownList2Values(string strDropDownList1Value)
{
DataTable objDataTable = new DataTable("GridDetails");
DataSet objDataSet = new DataSet();
DataRow objDR;

objDataSet.Tables.Add(objDataTable);
objDataTable.Columns.Add("Text", typeof(string));
objDataTable.Columns.Add("Values", typeof(string));

objDR = objDataTable.NewRow();
objDR["Text"] = "Data1" + " : " + strDropDownList1Value;
objDR["Values"] = "Data1" + " : " + strDropDownList1Value;
objDataTable.Rows.Add(objDR);

objDR = objDataTable.NewRow();
objDR["Text"] = "Data2" + " : " + strDropDownList1Value;
objDR["Values"] = "Data2" + " : " + strDropDownList1Value;
objDataTable.Rows.Add(objDR);

objDR = objDataTable.NewRow();
objDR["Text"] = "Data3" + " : " + strDropDownList1Value;
objDR["Values"] = "Data3" + " : " + strDropDownList1Value;
objDataTable.Rows.Add(objDR);

return objDataSet;
}

Step 6.Now go to your HTML page and write the following Javascript Function
<script language ="javascript" type="text/javascript">
function clientResponse(result,ctx,mm,nn)
{

var lstItems =document.all.DropDownList1;
var options = lstItems.getElementsByTagName("option");
var lstCustomers =document.all.DropDownList2;
// Clear out any content in the list.
lstCustomers.innerHTML= "";
// Get an array with a list of territory records.
var rows = result.split('');
for (var i = 0; i < rows.length - 1; ++i)
{
// Split each record into two fields.
var fields = rows[i].split('');
var customerID = fields[0];
var customerName = fields[1];
// Create the list item.
var option = document.createElement("option");
// Store the ID in the value attribute.
option.value = customerID;
// Show the description in the text of the list item.
option.innerHTML = customerName;
lstCustomers.appendChild(option);
}
}
function ErrorFunction(error , ctx)
{
alert("The Event Failed Becuase " + error);
}

</script>

Step 7.In the page directive write the following code
EnableEventValidation="false" as follows

<%@ Page Language="C#" EnableEventValidation="false" AutoEventWireup="true" CodeFile="Default2.aspx.cs" Inherits="Default2" %><%@ Page Language="C#" EnableEventValidation="false" AutoEventWireup="true" CodeFile="Default2.aspx.cs" Inherits="Default2" %>

Step 8.Now its time to run your application,Before Running it you just check your code behind file with the following complete Code
using System;
using System.Data;
using System.Configuration;
using System.Collections;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;

public partial class Default2 : System.Web.UI.Page, ICallbackEventHandler
{
private string earg;

protected void Page_Load(object sender, EventArgs e)
{
string eventRef = Page.ClientScript.GetCallbackEventReference(this, "document.getElementById('DropDownList1').value", "clientResponse", "null", "ErrorFunction", true);
DropDownList1.Attributes["onchange"] = eventRef;
}
#region ICallbackEventHandler Members
public string GetCallbackResult()
{
System.Text.StringBuilder sb1 = new System.Text.StringBuilder();
string strDropDownList1Value = this.earg;

DataSet ds = getDropDownList2Values(strDropDownList1Value);

for (int i = 0; i < ds.Tables[0].Rows.Count; i++)
{
sb1.Append(ds.Tables[0].Rows[i][0]);
sb1.Append("|");
sb1.Append(ds.Tables[0].Rows[i][1]);
sb1.Append("||");
}
return sb1.ToString();
}
public void RaiseCallbackEvent(string eventArgument)
{
this.earg = eventArgument;
}
#endregion
protected DataSet getDropDownList2Values(string strDropDownList1Value)
{
DataTable objDataTable = new DataTable("GridDetails");
DataSet objDataSet = new DataSet();
DataRow objDR;

objDataSet.Tables.Add(objDataTable);
objDataTable.Columns.Add("Text", typeof(string));
objDataTable.Columns.Add("Values", typeof(string));

objDR = objDataTable.NewRow();
objDR["Text"] = "Data1" + " : " + strDropDownList1Value;
objDR["Values"] = "Data1" + " : " + strDropDownList1Value;
objDataTable.Rows.Add(objDR);

objDR = objDataTable.NewRow();
objDR["Text"] = "Data2" + " : " + strDropDownList1Value;
objDR["Values"] = "Data2" + " : " + strDropDownList1Value;
objDataTable.Rows.Add(objDR);

objDR = objDataTable.NewRow();
objDR["Text"] = "Data3" + " : " + strDropDownList1Value;
objDR["Values"] = "Data3" + " : " + strDropDownList1Value;
objDataTable.Rows.Add(objDR);
return objDataSet;
}
}

Step9.Now run your application and change the values of your first dropdown ,Now you can see that the values of second dropdown will be changed without any postback

Disable Back Button in the browser

You can disable the functionality of the back button by the following function of javascript.Write the following code in your HTML page

<script language="javascript" type="text/javascript">
window.onload=onLoadFunctions;

function onLoadFunctions()
{
backButtonOverride();
}
function backButtonOverride()
{

setTimeout("backButtonOverrideBody()", 0);

}

function backButtonOverrideBody()
{

try {
history.forward();


}
catch (e)
{
// OK to ignore
}

setTimeout("backButtonOverrideBody()", 0);
}
</script>

Create Pages Using Object Model

Following example shows how to create a cutom HTML page using WSS Object model .

Step 1.Create a New console application
Step 2.Add a reference of Microsoft.Sharepoint.dll
Step 3 .Write the following code
using System;
using System.IO;
using Microsoft.SharePoint;

namespace CreateNewSitePage {
class Program {
static void Main() {

string sitePath = "http://manab:36069/sites/DevSite";
SPSite siteCollection = new SPSite(sitePath);
SPWeb site = siteCollection.RootWeb;

// write out new page in memory stream
MemoryStream stream = new MemoryStream();
StreamWriter writer = new StreamWriter(stream);
writer.WriteLine("<html><body >");
writer.WriteLine("Hello, World");
writer.WriteLine("</body></html >");
writer.Flush();

// add new page to site
site.Files.Add("hello.htm", stream);

}
}
}
Step 4.Now go to your sharepoint site and type the url as follows
http://manab:36069/sites/DevSite/

You will get the output as follows

Debugging WSS Components

Under normal conditions, WSS provides error messages intended for end users in a production environment. This means that WSS doesn’t automatically provide rich diagnostic information or helpful error messages to assist you when you are debugging your code. While you are developing WSS components such as custom application pages, you must modify the web.config file for the current Web application to enable debugging support and error messages that contain stack traces. Here’s a fragment of the web.config file that shows the three important attributes that have been changed from their default values to enable rich debugging support.

<configuration>
<SharePoint>
<SafeMode CallStack="true" />
</SharePoint>
<system.web>
<customErrors mode="Off" />
<compilation debug="true" />
</system.web>
</configuration>
While it is essential to modify the web.config file as shown here to enable debugging support, you will also find it occasionally necessary to return the web.config file to its original state. For example, you might create an application page that throws an exception or an event handler that cancels a user’s actions. By returning the web.config file to its original state, you can see how your code will actually behave in a production environment. Therefore, you should become comfortable with the act of changing the web.config file back and forth between debugging mode and standard end user mode.