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Using PagedDataSource For Paging
GridView, DetailsView or FormView controls are complex controls that have many pre-built features, including data paging or sorting. On opposite, Repeater or DataList offer more control over HTML output and they usually work faster than GridView, but better performances come with lack of complex GridView's features. Implementation of data paging and sorting is very simple with GridView control.
If you use Repeater or DataList, there is no built-in paging functionality and you need to build your own custom data pager since it is usually not acceptable to show hundreds or even thousands of records on single page. Fortunately, there is PagedDataSource class to help you with this task.
PagedDataSource class encapsulates paging functionality of data controls like GridView, FormView or DetailsView. If you ever worked with paging on these controls then using of PagedDataSource control will be familiar to you. Important class members, like AllowPaging, PageSize, PageCount property etc., have same names and use.
How to add paging to Repeater or DataList control using PagedDataSource control
Place one Repeater or DataList control on web form. For this example, I will use data from Products table of Northwind database. If you don't have Northwind database installed on your machine, use whichever database you have. It is not important what kind of data you show since we want to focus on paging.
Markup code for Repeater is pretty simple, it will show only product name. Bellow Repeater, add two LinkButton controls which will be used for navigation, like this:
<asp:Repeater ID="Repeater1" runat="server">
If you load Products table to DataTable object and bind to Repeater directly, it will show all 77 products on same page. But, we'll use PagedDataSource class implement paging. You can understand PagedDataSource as additional layer between data source control and data presentation control that filter record set and returns only one selected page. Here is the code:
[ C# ]
[ VB.NET ]
Of course, you are not limited to Repeater control. With PagedDataSource you can use DataList, RadioButtonList, CheckBoxList etc., even GridView in some cases, for example if you need different pager on top and on bottom of the page. GridView's PagerTemplate allows you to customize paging but it shows same pager on top and on the bottom. With PagedDataSource you can create two pagers with different styling.
Using PagedDataSource without callbacks
Instead of using Button, LinkButton or other ASP.NET server control, you can create navigation with simple HTML links. In this case, we'll place page variable in query string. Instead of LinkButton controls used in previous example, this time place two PlaceHolder controls phNext and phPrevious (here we'll add HTML links). Code for BindData procedure and Page_Load will look a little different:
[ C# ]protected void Page_Load(object sender, EventArgs e)
// Get current page from query string variable
string SelectedPage = Request.QueryString["page"];
// If no page selected, show first page by default
if (SelectedPage == null)
SelectedPage = "0";
private void BindData(int SelectedPage)
// Step 1 and 2 are the same as in previous example
// Step 3: Bind PagedDataSource to Repeater as before
Repeater1.DataSource = pds;
// Create static HTML links for paging
litNext.Text = "<b>Next</b>";
litNext.Text = @"<a href=""?page=" + (SelectedPage + 1).ToString() +
litPrevious.Text = "<b>Previous</b>";
litPrevious.Text = @"<a href=""?page=" + (SelectedPage - 1).ToString() +
[ VB.NET ]
Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
PagedDataSource class members
PagedDataSource class is located in System.Web.UI.WebControls namespace in System.Web assembly, so you don't need to add any new reference or import namespace.
These are few most important PagedDataSource properties:
Boolean [ get, set ] - default value is false. Like in GridView, AllowPaging determines is paging enabled. You can turn on paging if set AllowPaging to true.
Int32 [ get, set ] - default value is 0. CurrentPageIndex represents index of current page. We usually increment or decrement this property in "Next page" and "Previous page" links.
IEnumerable [ get, set ] - Source of the data, for example DataView. Classes that don't support indexing of records, like DataReader can't be used with PagedDataSource.
Boolean [ get ] - Returns true if current page is first page in data set. Otherwise, returns false.
Boolean [ get ] - Determines is current page last page in data set.
Boolean [ get ] - Returns true if AllowPaging is true, otherwise false.
Int32 [ get ] - PageCount returns total number of pages.
Int32 [ get, set ] - default value is 10. PageSize determines how many records are shown per page.
For complete list of available PagedDataSource class members check MSDN.
Optmization problems when PagedDataSource is used
If you have large table, using of PagedDataSource can cause performance problems. Although PagedDataSource provides only one page to Repeater, DataList or some other control, in behind it works with all records. To show one page with 5 or 10 rows you need to open thousands or even millions of rows in memory. This is a waste of server resources and could lead to slow execution of ASP.NET application.
What is "too large" table for PagedDataSource depends of many factors, not just how much records you have. If you are on shared hosting with hundreds of sites and databases on same server, then even table with few thousands of records can cause PagedDataSource to work slowly. Sometimes, you can improve performances by using caching, but in reality most users don't browse more than few first pages and loading of thousands of pages in memory is often bad idea.
To create scalable paging solution that works as fast as possible, you need to load only what is necessary; in other words, you need to load only current page. You can achieve this with ad-hoc SQL queries or using stored procedures. Both methods are described in SQL Queries For Paging In ASP.NET and Paging With SQL Server Stored Procedures In ASP.NET tutorials.
Paging and SEO (Search Engine Optimization) issues
Simple solution for search engines is to use HTML links for navigation and have page variables in query string, like in second example. Even better option is to employ some method of URL rewriting in ASP.NET to get nice pager links without query strings used.
Another problem with callback occurs if visitor tries to bookmark certain page. Since URL stays the same, visitor can bookmark only first page. If query strings or URL rewriting are used, every page has different URL and it's easy to add it to favorites.
PagedDataSource class remarks
PagedDataSource inherits ICollection, IEnumerable and ITypeList interfaces. That means that could work with data sources that could be counted or indexed, like DataView, List or HashTable, but it can't work with DataReader, SqlDataSource etc. Even DataTable can't be used directly, you need to bind PagedDataSource to DataView type, for example YourDataTable.DefaultView.
Going professional with SEO Pager control
PagedDataSource has few drawbacks. First is that it doesn't create any HTML output, so to create pager you must make all buttons, numbers, jump to specific page element, use CSS styling etc. This could demand significant time if your pager is anything more complex than just Previous, Next buttons. Another serious problem is bad performances if PagedDataSource works with large tables. Even if your site currently works well, you need to consider possible increase of data in the future or increase of visits if your site becomes popular.
To implement data paging fast, but in the same time scalable, nice looking, optimized for search engines and customizable, we created SEO Pager control. SEO Pager can work with PagedDataSource, but you can also easily switch to stored procedures if your site grows. Also, SEO pager can use callbacks, query strings or URL rewriting to better match your web site. Finally, SEO Pager enables different HTML output. There are predefined layouts to enable paging with numbers, tags, images, vertical paging, alphabetic paging etc. and also custom template that can be used to make pager in practically unlimited ways.
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