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Load Data From Server While Scrolling Using jQuery AJAX

By , 26 Apr 2012
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Introduction

This article will demonstrate how to load data from the server while scrolling. Loading data from the server using AJX will help any application in improving its performance because data which is displayed on the screen alone is loaded the first time and more data, if required, will get loaded from the server as the user scrolls.

Background

Facebook is the application which inspired me to write code to load data from the server while scrolling. While browsing Facebook, I was amazed to see that as I scrolled on the page, new data from the server got appended to the existing one. I became curious about implementing the same functionality in C#. I searched for information, but did not find any article or blog on doing this in C#. Of course, there were a few articles for Java and PHP. I read them carefully and started writing code in C#. As it worked successfully I thought I'd share it, so I am posting it here.

The code

To implement the load on scroll functionality, we will require very few lines of code. A WebMethod that will be called from the client side which returns the content to append while scrolling, and a client side function (document.ready) where we will bind the scroll event to load data from the server. Let us see these server and client side methods in detail.

Server method: This method is used to get data from the database or any source and prepares an HTML string depending on the control you are using for appending data to. Here I have just added a message with the serial number.

[WebMethod]
public static string  GetDataFromServer() 
{ 
    string resp = string.Empty; 
    for(int i = 0; i <= 10; i++)
    {
        resp += "<p><span>"  + counter++ + 
          "</span> This content is dynamically appended " + 
          "to the existing content on scrolling.</p>" ; 
    } 
    return resp; 
} 

If you want to load data from database you can modify your method as follows : 

[WebMethod]
public static string GetDataFromServer()
    {
        DataSet ds = new DataSet();
 
        // Set value of connection string here
        string strConnectionString = ""; // Insert your connection string value here
        SqlConnection con = new SqlConnection(strConnectionString);
 
        // Write the select command value as first parameter
        SqlCommand command = new SqlCommand("SELECT * FROM Person", con);
        SqlDataAdapter adp = new SqlDataAdapter(command);
int retVal = adp.Fill(ds);
 
        string resp = string.Empty;
for (int i = 1; i <= ds.Tables[0].Rows.Count; i++)
        {
            string strComment = string.Empty;
if (ds.Tables != null)
            {
if (ds.Tables[0] != null)
                {
if (ds.Tables[0].Rows.Count > 0)
                    {
if (ds.Tables[0].Rows.Count >= i - 1)
                        {
if (ds.Tables[0].Rows[i - 1][0] != DBNull.Value)
                            {
                                strComment = ds.Tables[0].Rows[i - 1][0].ToString();
                            }
                        }
                    }
                }
            }
            resp += "<p><span>" + counter++ + "</span> " + strComment + "</p>";
        }
return resp;
    }  

Client method: At the client side, I have used the document.ready method in which I have registered event binding for scroll on div. I have used two div elements: mainDiv and wrapperDiv. I have registered the scroll event for mainDiv and append dynamic data to wrapperDiv.

$(document).ready( 
function()
{
$contentLoadTriggered = false;
$("#mainDiv").scroll(
function()
{
if($("#mainDiv").scrollTop() >= ($("#wrapperDiv").height() - 
   $("#mainDiv").height()) &&
   $contentLoadTriggered == false)
   $contentLoadTriggered == false)
{
$contentLoadTriggered = true;
$.ajax(
{
type: "POST",
url: "LoadOnScroll.aspx/GetDataFromServer",
data: "{}",
contentType: "application/json; charset=utf-8",
dataType: "json",
async: true,
cache: false,
success: function (msg) 
{
$("#wrapperDiv").append(msg.d);
$contentLoadTriggered = false;
},
error: function (x, e)
{
alert("The call to the server side failed. " +
x.responseText);
}
}
);
}
}
);
}
);

Here, to check whether the scroller has moved at the bottom, the following condition is used.

if($("#mainDiv").scrollTop() >= 
  ($("#wrapperDiv").height() - $("#mainDiv").height()) &&
   $contentLoadTriggered == false)

This condition will identify whether the scroller has moved at the bottom or not. If it has moved at the bottom, dynamic data will get loaded from the server and get appended to wrapperDiv. The client script to append data to the desired div element is written in the script to run when the asynchronous call results in success.

success: function (msg)
{
$("#wrapperDiv").append(msg.d);
$contentLoadTriggered = false;
}

Here one thing you will notice is that the request will go to the server only when the user has scrolled at the bottom.

I have attached the sample application with this article.

Output

LoadOnScroll/LOS1.JPG

LoadOnScroll/LOS2.JPG

History

First version.

License

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

About the Author

Praveen Meghwal
Software Developer (Senior)
India India
No Biography provided

Comments and Discussions

 
Questionexplain some lines mean lines Pinmembermaheshbisht30-Sep-12 22:53 
GeneralMy vote of 5 PinmemberPrasad J2-Aug-12 19:42 
GeneralMy vote of 5 PinmemberTushar_Patil18-May-12 2:41 
QuestionHmmm.. Not a real-world example PinmemberClutchplate10-May-12 6:38 
Questionfor jQuery AJAX load data PinmemberKien Nguyen Ngoc8-May-12 5:51 
AnswerRe: for jQuery AJAX load data PinmemberPraveen Meghwal9-May-12 18:56 
SuggestionMy vote of 5 PinmemberAkram El Assas26-Apr-12 22:34 
GeneralRe: My vote of 5 PinmemberPraveen Meghwal29-Apr-12 18:33 
GeneralMy vote of 5 PinmemberMonjurul Habib26-Apr-12 21:10 
GeneralRe: My vote of 5 PinmemberPraveen Meghwal29-Apr-12 18:33 
GeneralMy vote of 5 PinmemberManish Sharma16-Apr-12 23:16 
GeneralRe: My vote of 5 PinmemberPraveen Meghwal29-Apr-12 18:33 
Generalits very usefull Pinmembersuraj mahajan27-Mar-12 3:06 
GeneralRe: its very usefull PinmemberPraveen Meghwal27-Mar-12 19:23 
QuestionMy vote of 5 PinmemberNguyen Quy Minh22-Feb-12 5:10 
AnswerRe: My vote of 5 PinmemberPraveen Meghwal22-Feb-12 20:05 
QuestionThanks for sharing such a nice article. PinmemberZaheer Mazhar5-Jan-12 5:37 
AnswerRe: Thanks for sharing such a nice article. PinmemberZaheer Mazhar5-Jan-12 6:22 
I only want to ask one thing that if i want to assiciate this scroll functionality with right side scroller like in facebook, then which code we will need to change? I don't want to use little maindiv, in place of this i want to use the default scrolling in browser and want to associate callback based on that scroller. Can you guide me.
GeneralRe: Thanks for sharing such a nice article. PinmemberPraveen Meghwal8-Jan-12 22:56 
QuestionAdding SQL data PinmemberDamo B13-Dec-11 5:46 
AnswerRe: Adding SQL data PinmemberPraveen Meghwal8-Jan-12 22:59 
GeneralMy vote of 3 Pinmemberbasskaran27-Nov-11 22:26 
GeneralRe: My vote of 3 PinmemberPraveen Meghwal15-Dec-11 21:17 
GeneralMy vote of 5 Pinmembermhamad zarif29-Oct-11 7:46 
GeneralRe: My vote of 5 PinmemberPraveen Meghwal15-Dec-11 21:17 

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