In this blog post, I am going the demonstrate the steps
involved in implementing “Infinite Scroll” in web application for loading
images just like in Bing and Google image search.
Infinite Scroll –
Infinite scroll has been called auto paganize/endless pages. But essentially it
is pre-fetching content from a subsequent page and adding it directly to the
user’s current page.
One of the most annoying thing when working with large data
is how to continuously loading the data on demand to your page?
The common solution is paging but paging itself will not
help too much you can end with hundreds or thousands of pages. So a new
solution now is on the surface and it's called "Infinite Scroll". It allows
you to load chunk of data when you scroll down of the page and inject it inside
the page, it will load data each time you scrolling down on the page.
Step 1: Include jquery library file. You can download the current version
of “jquery” library from this link http://docs.jquery.com/Downloading_jQuery
<script type="text/javascript"
src="Scripts/jquery-x.x.x.min.js"></script>
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Step 2: Add Images
folder to the web project which contains images that is loaded on runtime in
the website.
Step 3: Add below
designer code to create a list view to load the images initially.
<asp:ListView
ID="ListView1" runat="server" EnableModelValidation="True">
<LayoutTemplate>
<ul id="itemPlaceholderContainer"
runat="server"
class="thumb">
<asp:PlaceHolder runat="server"
ID="itemPlaceholder" />
</ul>
</LayoutTemplate>
<ItemTemplate>
<asp:Image ID="Image1" runat="server" ImageUrl='<%#
Eval("image")%>' />
</ItemTemplate>
</asp:ListView>
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Step 4: Fill the
list view with images using below code on Page Load event.
protected void Page_Load(object
sender, EventArgs e)
{
if (!IsPostBack)
{
FillListView(48);
}
}
//Fill images in the list view
private void FillListView(int Rows)
{
string Imagespath = HttpContext.Current.Server.MapPath("~/Images/");
string SitePath = HttpContext.Current.Server.MapPath("~");
//Load image
files using linq query
var Files = (from file in Directory.GetFiles(Imagespath) select new { image = file.Replace(SitePath, "~/") }).Take(Rows);
ListView1.DataSource
= Files.ToList();
ListView1.DataBind();
}
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Step 5: For now
we have loaded 48 images to the list view. In the next step we are going to use
the script and the code behind to load the next set of images dynamically on
scroll down just like in Google and Bing.
a.
Add below script the aspx
file
<script type="text/javascript">
$(document).ready(function () {
var Skip = 48; //Number of image to skip
var Take = 14; //
function
Load(Skip, Take) {
//Post below loader image as progress bar
$('#divPostsLoader').html('<img src="ProgressBar/ajax-loader.gif">');
//send a query to server side
to present new content
$.ajax({
type: "POST",
url:
"Default.aspx/LoadImages", //Call the LoadImage method in the code behind
data: "{ Skip:" + Skip + ", Take:" + Take + "
}",
contentType:
"application/json; charset=utf-8",
dataType: "json",
success: function (data) {
if (data != "") {
$('.thumb').append(data.d); //Append the retrieved
images next to list view
}
$('#divPostsLoader').empty();
}
})
};
//Larger
thumbnail preview
//When
scroll down, the scroller is at the bottom with the
function below and fire the lastPostFunc function
$(window).scroll(function () {
if
($(window).scrollTop() == ($(document).height() -
$(window).height())) {
Load(Skip, Take);
Skip = Skip + 14;
}
});
});
</script>
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b.
Add below method next to FillListView(). This method
will the next set of images provided number of images to skip and the next set
of images to take.
[WebMethod]
public
static string LoadImages(int
Skip, int Take)
{
System.Threading.Thread.Sleep(2000);
StringBuilder GetImages = new StringBuilder();
string Imagespath = HttpContext.Current.Server.MapPath("~/Images/");
string SitePath = HttpContext.Current.Server.MapPath("~");
var Files = (from file in Directory.GetFiles(Imagespath) select new { image = file.Replace(SitePath, "~/") }).Skip(Skip).Take(Take);
foreach (var file in Files)
{
var imageSrc = file.image.Replace("\\",
"/").Substring(1); //Remove First '/' from image path
GetImages.Append(" ");
GetImages.AppendFormat(string.Format("<img src='{0}'/>", imageSrc)); GetImages.Append("
");
}
return GetImages.ToString();
}
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Final Code:
Default.aspx
<%@ Page Language="C#" AutoEventWireup="true"
CodeBehind="Default.aspx.cs"
Inherits="InfiniteScroll.Default" %>
<!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 id="Head1" runat="server">
<title>Infinite Scroll</title>
<script
type="text/javascript" src="Scripts/jquery-1.4.1.min.js"></script>
<script
type="text/javascript">
$(document).ready(function () {
var Skip = 48; //Number of skipped image
var Take = 14; //
function
Load(Skip, Take) {
$('#divPostsLoader').html('<img src="ProgressBar/ajax-loader.gif">');
//send a query to server side to present new content
$.ajax({
type: "POST",
url: "Default.aspx/LoadImages",
data: "{ Skip:" + Skip + ", Take:" + Take + "
}",
contentType: "application/json;
charset=utf-8",
dataType: "json",
success: function (data) {
if (data != "") {
$('.thumb').append(data.d);
}
$('#divPostsLoader').empty();
}
})
};
//Larger thumbnail preview
//When
scroll down, the scroller is at the bottom with the
function below and fire the lastPostFunc function
$(window).scroll(function () {
if
($(window).scrollTop() == ($(document).height() -
$(window).height())) {
Load(Skip, Take);
Skip = Skip + 14;
}
});
});
</script>
<style
type="text/css">
img { border:"none"; margin:"auto"}
.container {
padding:"2px"; }
</style>
</head>
<body>
<form
id="form1" runat="server">
<div>
<div
class="header">
<div
class="title">
<h1>
Infinite Scroll Example
</h1>
</div>
</div>
<div>
<asp:ListView ID="ListView1" runat="server"
EnableModelValidation="True">
<LayoutTemplate>
<ul id="itemPlaceholderContainer"
runat="server"
class="thumb">
<asp:PlaceHolder runat="server"
ID="itemPlaceholder" />
</ul>
</LayoutTemplate>
<ItemTemplate>
<asp:Image
ID="Image1" runat="server" ImageUrl='<%# Eval("image")%>'
/>
</ItemTemplate>
</asp:ListView>
<div
style="margin-left: auto; margin-right: auto; width: 120px;"
id="divPostsLoader">
</div>
</div>
</div>
</form>
</body>
</html>
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Default.aspx.cs
using System;
using System.Linq;
using System.Web;
using System.Web.Services;
using System.Text;
using System.IO;
namespace InfiniteScroll
{
public partial
class Default : System.Web.UI.Page
{
protected
void Page_Load(object sender, EventArgs
e)
{
if (!IsPostBack)
{
Fill_List(48);
}
}
private void
Fill_List(int Rows)
{
string Imagespath = HttpContext.Current.Server.MapPath("~/Images/");
string SitePath = HttpContext.Current.Server.MapPath("~");
var Files = (from file in Directory.GetFiles(Imagespath) select new { image = file.Replace(SitePath, "~/") }).Take(Rows);
ListView1.DataSource = Files.ToList();
ListView1.DataBind();
}
[WebMethod]
public
static string LoadImages(int
Skip, int Take)
{
System.Threading.Thread.Sleep(2000);
StringBuilder GetImages = new StringBuilder();
string Imagespath = HttpContext.Current.Server.MapPath("~/Images/");
string SitePath = HttpContext.Current.Server.MapPath("~");
var Files = (from file in Directory.GetFiles(Imagespath) select new { image = file.Replace(SitePath, "~/") }).Skip(Skip).Take(Take);
foreach (var file in Files)
{
var imageSrc = file.image.Replace("\\",
"/").Substring(1); //Remove First '/' from image path
GetImages.Append(" ");
GetImages.AppendFormat(string.Format("<img src='{0}'/>", imageSrc));
GetImages.Append(" ");
}
return GetImages.ToString();
}
}
}
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This post provides just an introduction (basic) on the
usage of “Infinite Scroll” feature. However the likes (immense potential) of
which we have already seen in “Facebook updates”, “Flip kart item search” and “Bing
and Google image search” etc.,.
References:
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