Paging in ASP.NET has been relatively easy with stock controls supporting basic paging functionality. However, recently I built an MVC application and one of
the things I ran into was that I HAD TO build manual paging support into a few of my pages. Dealing with list controls and rendering markup is easy enough, but doing paging is a
little more involved. I ended up with a small but flexible component that can be dropped anywhere. As it turns out
the task of creating a semi-generic Pager control for MVC was fairly easily. Now I’m back to working in Web Forms and thought to myself that
the way I created
the pager in MVC actually would also work in ASP.NET – in fact quite a bit easier since
the whole thing can be conveniently wrapped up into an easily reusable control. A standalone pager would provider easier reuse in various pages and a more consistent pager display regardless of what kind of 'control’
the pager is associated with. Why a Pager Control? At first blush it might sound silly to create a new pager control – after all Web Forms has pretty decent paging support, doesn’t it? Well, sort of. Yes
the GridView control has automatic paging built in and
the ListView control has
the related DataPager control.
The built in ASP.NET paging has several issues though: Postback and JavaScript requirements If you look at paging links in ASP.NET they are always postback links with javascript:__doPostback() calls that go back to
the server. While that works fine and actually has some benefit like
the fact that paging saves changes to
the page and post them back, it’s not very SEO friendly. Basically if you use javascript based navigation nosearch engine will follow
the paging links which effectively cuts off list content on
the first page.
The DataPager control does support GET based links via
the QueryStringParameter property, but
the control is effectively tied to
the ListView control (which is
the only control that implements IPageableItemContainer). DataSource Controls required for Efficient Data Paging Retrieval
The only way you can get paging to work efficiently where only
the few records you display on
the page are queried for and retrieved from
the database you have to use a DataSource control - only
the Linq and Entity DataSource controls support this natively. While you can retrieve this data yourself manually, there’s no way to just assign
the page number and render
the pager based on this custom subset. Other than that default paging requires a full resultset for ASP.NET to filter
the data and display only a subset which can be very resource intensive and wasteful if you’re dealing with largish resultsets (although I’m a firm believer in returning actually usable sets :-}). If you use your own business layer that doesn’t fit an ObjectDataSource you’re SOL. That’s a real shame too because with LINQ based querying it’s real easy to retrieve a subset of data that is just
the data you want to display but
the native Pager functionality doesn’t support just setting properties to display just
the subset AFAIK. DataPager is not Free Standing
The DataPager control is
the closest thing to a decent Pager implementation that ASP.NET has, but alas it’s not a free standing component – it works off a related control and
the only one that it effectively supports from
the stock ASP.NET controls is
the ListView control. This means you can’t use
the same data pager formatting for a grid and a list view or vice versa and you’re always tied to
the control. Paging Events In order to handle paging you have to deal with paging events.
The events fire at specific time instances in
the page pipeline and because of this you often have to handle data binding in a way to work around
the paging events or else end up double binding your data sources based on paging. Yuk. Styling
The GridView pager is a royal pain to beat into submission for styled rendering.
The DataPager control has many more options and template layout and it renders somewhat cleaner, but it too is not exactly easy to get a decent display for. Not a Generic Solution
The problem with
the ASP.NET controls too is that it’s not generic. GridView, DataGrid use their own internal paging, ListView can use a DataPager and if you want to manually create data layout – well you’re on your own. IOW, depending on what you use you likely have very different looking Paging experiences. So, I figured I’ve struggled with this once too many and finally sat down and built a Pager control.
The Pager Control My goal was to create a totally free standing control that has no dependencies on other controls and certainly no requirements for using DataSource controls.
The idea is that you should be able to use this pager control without any sort of data requirements at all – you should just be able to set properties and be able to display a pager.
The Pager control I ended up with has
the following features: Completely free standing Pager control – no control or data dependencies Complete manual control – Pager can render without any data dependency Easy to use: Only need to set PageSize, ActivePage and TotalItems Supports optional filtering of IQueryable for efficient queries and Pager rendering Supports optional full set filtering of IEnumerable<T> and DataTable Page links are plain HTTP GET href Links Control automatically picks up Page links on
the URL and assigns them (automatic page detection no page index changing events to hookup) Full CSS Styling support On
the downside there’s no templating support for
the control so
the layout of
the pager is relatively fixed. All elements however are stylable and there are options to control
the text, and layout options such as whether to display first and last pages and
the previous/next buttons and so on. To give you an idea what
the pager looks like, here are two differently styled examples (all via CSS):
The markup for these two pagers looks like this: <ww:Pager runat="server" id="ItemPager"
PageSize="5"
PageLinkCssClass="gridpagerbutton"
SelectedPageCssClass="gridpagerbutton-selected"
PagesTextCssClass="gridpagertext"
CssClass="gridpager"
RenderContainerDiv="true"
ContainerDivCssClass="gridpagercontainer"
MaxPagesToDisplay="6"
PagesText="Item Pages:"
NextText="next"
PreviousText="previous"
/>
<ww:Pager runat="server" id="ItemPager2"
PageSize="5"
RenderContainerDiv="true"
MaxPagesToDisplay="6" />
The latter example uses default style settings so it there’s not much to set.
The first example on
the other hand explicitly assigns custom styles and overrides a few of
the formatting options.
Styling
The styling is based on a number of CSS classes of which
the the main pager, pagerbutton and pagerbutton-selected classes are
the important ones. Other styles like pagerbutton-next/prev/first/last are based on
the pagerbutton style.
The default styling shown for
the red outlined pager looks like this:
.pagercontainer
{
margin: 20px 0;
background: whitesmoke;
padding: 5px;
}
.pager
{
float: right;
font-size: 10pt;
text-align: left;
}
.pagerbutton,.pagerbutton-selected,.pagertext
{
display: block;
float: left;
text-align: center;
border: solid 2px maroon;
min-width: 18px;
margin-left: 3px;
text-decoration: none;
padding: 4px;
}
.pagerbutton-selected
{
font-size: 130%;
font-weight: bold;
color: maroon;
border-width: 0px;
background: khaki;
}
.pagerbutton-first
{
margin-right: 12px;
}
.pagerbutton-last,.pagerbutton-prev
{
margin-left: 12px;
}
.pagertext
{
border: none;
margin-left: 30px;
font-weight: bold;
}
.pagerbutton a
{
text-decoration: none;
}
.pagerbutton:hover
{
background-color: maroon;
color: cornsilk;
}
.pagerbutton-prev
{
background-image: url(images/prev.png);
background-position: 2px center;
background-repeat: no-repeat;
width: 35px;
padding-left: 20px;
}
.pagerbutton-next
{
background-image: url(images/next.png);
background-position: 40px center;
background-repeat: no-repeat;
width: 35px;
padding-right: 20px;
margin-right: 0px;
}
Yup that’s a lot of styling settings although not all of them are required.
The key ones are pagerbutton, pager and pager selection.
The others (which are implicitly created by
the control based on
the pagerbutton style) are for custom markup of
the ‘special’ buttons.
In my apps I tend to have two kinds of pages: Those that are associated with typical ‘grid’ displays that display purely tabular data and those that have a more looser list like layout.
The two pagers shown above represent these two views and
the pager and gridpager styles in my standard style sheet reflect these two styles.
Configuring
the Pager with Code
Finally lets look at what it takes to hook up
the pager. As mentioned in
the highlights
the Pager control is completely independent of other controls so if you just want to display a pager on its own it’s as simple as dropping
the control and assigning
the PageSize, ActivePage and either TotalPages or TotalItems.
So for this markup:
<ww:Pager runat="server" id="ItemPagerManual"
PageSize="5"
MaxPagesToDisplay="6"
/>
I can use code as simple as:
ItemPagerManual.PageSize = 3;
ItemPagerManual.ActivePage = 4;ItemPagerManual.TotalItems = 20;
Note that ActivePage is not required - it will automatically use any Page=x query string value and assign it, although you can override it as I did above. TotalItems can be any value that you retrieve from a result set or manually assign as I did above.
A more realistic scenario based on a LINQ to SQL IQueryable result is even easier. In this example, I have a UserControl that contains a ListView control that renders IQueryable data. I use a User Control here because there are different views
the user can choose from with each view being a different user control. This incidentally also highlights one of
the nice features of
the pager: Because
the pager is independent of
the control I can put
the pager on
the host page instead of into each of
the user controls. IOW, there’s only one Pager control, but there are potentially many user controls/listviews that hold
the actual display data.
The following code demonstrates how to use
the Pager with an IQueryable that loads only
the records it displays: protected voidPage_Load(objectsender, EventArgs e)
{
Category = Request.Params["Category"] ?? string.Empty;
IQueryable<wws_Item> ItemList = ItemRepository.GetItemsByCategory(Category);
// Update
the page and filter
the list down
ItemList = ItemPager.FilterIQueryable<wws_Item>(ItemList);
// Render user control with a list view
Control ulItemList = LoadControl("~/usercontrols/" + App.Configuration.ItemListType + ".ascx");
((IInventoryItemListControl)ulItemList).InventoryItemList = ItemList;
phItemList.Controls.Add(ulItemList); // placeholder
}
The code uses a business object to retrieve Items by category as an IQueryable which means that
the result is only an expression tree that hasn’t execute SQL yet and can be further filtered. I then pass this IQueryable to
the FilterIQueryable() helper method of
the control which does two main things:
Filters
the IQueryable to retrieve only
the data displayed on
the active page
Sets
the Totaltems property and calculates TotalPages on
the Pager
and that’s it! When
the Pager renders it uses those values, plus
the PageSize and ActivePage properties to render
the Pager.
In addition to IQueryable there are also filter methods for IEnumerable<T> and DataTable, but these versions just filter
the data by removing rows/items from
the entire already retrieved data.
Output Generated and Paging Links
The output generated creates pager links as plain href links. Here’s what
the output looks like:
<div id="ItemPager" class="pagercontainer">
<div class="pager">
<span class="pagertext">Pages: </span><a href="http://localhost/WestWindWebStore/itemlist.aspx?Page=1" class="pagerbutton" />1</a>
<a href="http://localhost/WestWindWebStore/itemlist.aspx?Page=2" class="pagerbutton" />2</a>
<a href="http://localhost/WestWindWebStore/itemlist.aspx?Page=3" class="pagerbutton" />3</a>
<span class="pagerbutton-selected">4</span>
<a href="http://localhost/WestWindWebStore/itemlist.aspx?Page=5" class="pagerbutton" />5</a>
<a href="http://localhost/WestWindWebStore/itemlist.aspx?Page=6" class="pagerbutton" />6</a>
<a href="http://localhost/WestWindWebStore/itemlist.aspx?Page=20" class="pagerbutton pagerbutton-last" />20</a> <a href="http://localhost/WestWindWebStore/itemlist.aspx?Page=3" class="pagerbutton pagerbutton-prev" />Prev</a> <a href="http://localhost/WestWindWebStore/itemlist.aspx?Page=5" class="pagerbutton pagerbutton-next" />Next</a></div>
<br clear="all" />
</div>
</div>
The links point back to
the current page and simply append a Page= page link into
the page. When
the page gets reloaded with
the new page number
the pager automatically detects
the page number and automatically assigns
the ActivePage property which results in
the appropriate page to be displayed.
The code shown in
the previous section is all that’s needed to handle paging.
Note that HTTP GET based paging is different than
the Postback paging ASP.NET uses by default. Postback paging preserves modified page content when clicking on pager buttons, but this control will simply load a new page – no page preservation at this time.
The advantage of not using Postback paging is that
the URLs generated are plain HTML links that a search engine can follow where __doPostback() links are not.
Pager with a Grid
The pager also works in combination with grid controls so it’s easy to bypass
the grid control’s paging features if desired. In
the following example I use a gridView control and binds it to a DataTable result which is also filterable by
the Pager control.
The very basic plain vanilla ASP.NET grid markup looks like this:
<div style="width: 600px; margin: 0 auto;padding: 20px; ">
<asp:DataGrid runat="server" AutoGenerateColumns="True"
ID="gdItems" CssClass="blackborder" style="width: 600px;">
<AlternatingItemStyle CssClass="gridalternate" />
<HeaderStyle CssClass="gridheader" />
</asp:DataGrid>
<ww:Pager runat="server" ID="Pager"
CssClass="gridpager"
ContainerDivCssClass="gridpagercontainer"
PageLinkCssClass="gridpagerbutton"
SelectedPageCssClass="gridpagerbutton-selected"
PageSize="8"
RenderContainerDiv="true"
MaxPagesToDisplay="6" />
</div>
and looks like this when rendered:
using custom set of CSS styles.
The code behind for this code is also very simple:
protected void Page_Load(object sender, EventArgs e)
{
string category = Request.Params["category"] ?? "";
busItem itemRep = WebStoreFactory.GetItem();
var items = itemRep.GetItemsByCategory(category)
.Select(itm => new {Sku = itm.Sku, Description = itm.Description});
// run query into a DataTable for demonstration
DataTable dt = itemRep.Converter.ToDataTable(items,"TItems");
// Remove all items not on
the current page
dt = Pager.FilterDataTable(dt,0);
// bind and display
gdItems.DataSource = dt;
gdItems.DataBind();
}
A
little contrived I suppose since
the list could already be bound from
the list of elements, but this is to demonstrate that you can also bind against a DataTable if your business layer returns those.
Unfortunately there’s no way to filter a DataReader as it’s a one way forward only reader and
the reader is required by
the DataSource to perform
the bindings. However, you can still use a DataReader as long as your business logic filters
the data prior to rendering and provides a total item count (most likely as a second query).
Control Creation
The control itself is a pretty brute force ASP.NET control. Nothing clever about this other than some basic rendering logic and some simple calculations and update routines to determine which buttons need to be shown. You can take a look at
the full code from
the West Wind Web Toolkit’s Repository (note there are a few dependencies).
To give you an idea how
the control works here is
the Render() method:
/// <summary>
/// overridden to handle custom pager rendering for runtime and design time
/// </summary>
/// <param name="writer"></param>
protected override void Render(HtmlTextWriter writer)
{
base.Render(writer);
if (TotalPages == 0 && TotalItems > 0)
TotalPages = CalculateTotalPagesFromTotalItems();
if (DesignMode)
TotalPages = 10;
// don't render pager if there's only one page
if (TotalPages < 2)
return;
if (RenderContainerDiv)
{
if (!string.IsNullOrEmpty(ContainerDivCssClass))
writer.AddAttribute("class", ContainerDivCssClass);
writer.RenderBeginTag("div");
}
// main pager wrapper
writer.WriteBeginTag("div");
writer.AddAttribute("id", this.ClientID);
if (!string.IsNullOrEmpty(CssClass))
writer.WriteAttribute("class", this.CssClass);
writer.Write(HtmlTextWriter.TagRightChar + "\r\n");
// Pages Text
writer.WriteBeginTag("span");
if (!string.IsNullOrEmpty(PagesTextCssClass))
writer.WriteAttribute("class", PagesTextCssClass);
writer.Write(HtmlTextWriter.TagRightChar);
writer.Write(this.PagesText);
writer.WriteEndTag("span");
// if
the base url is empty use
the current URL
FixupBaseUrl();
// set _startPage and _endPage
ConfigurePagesToRender();
// write out first page link
if (ShowFirstAndLastPageLinks && _startPage != 1)
{
writer.WriteBeginTag("a");
string pageUrl = StringUtils.SetUrlEncodedKey(BaseUrl, QueryStringPageField, (1).ToString());
writer.WriteAttribute("href", pageUrl);
if (!string.IsNullOrEmpty(PageLinkCssClass))
writer.WriteAttribute("class", PageLinkCssClass + " " + PageLinkCssClass + "-first");
writer.Write(HtmlTextWriter.SelfClosingTagEnd);
writer.Write("1");
writer.WriteEndTag("a");
writer.Write(" ");
}
// write out all
the page links
for (int i = _startPage; i < _endPage + 1; i++)
{
if (i == ActivePage)
{
writer.WriteBeginTag("span");
if (!string.IsNullOrEmpty(SelectedPageCssClass))
writer.WriteAttribute("class", SelectedPageCssClass);
writer.Write(HtmlTextWriter.TagRightChar);
writer.Write(i.ToString());
writer.WriteEndTag("span");
}
else
{
writer.WriteBeginTag("a");
string pageUrl = StringUtils.SetUrlEncodedKey(BaseUrl, QueryStringPageField, i.ToString()).TrimEnd('&');
writer.WriteAttribute("href", pageUrl);
if (!string.IsNullOrEmpty(PageLinkCssClass))
writer.WriteAttribute("class", PageLinkCssClass);
writer.Write(HtmlTextWriter.SelfClosingTagEnd);
writer.Write(i.ToString());
writer.WriteEndTag("a");
}
writer.Write("\r\n");
}
// write out last page link
if (ShowFirstAndLastPageLinks && _endPage < TotalPages)
{
writer.WriteBeginTag("a");
string pageUrl = StringUtils.SetUrlEncodedKey(BaseUrl, QueryStringPageField, TotalPages.ToString());
writer.WriteAttribute("href", pageUrl);
if (!string.IsNullOrEmpty(PageLinkCssClass))
writer.WriteAttribute("class", PageLinkCssClass + " " + PageLinkCssClass + "-last");
writer.Write(HtmlTextWriter.SelfClosingTagEnd);
writer.Write(TotalPages.ToString());
writer.WriteEndTag("a");
}
// Previous link
if (ShowPreviousNextLinks && !string.IsNullOrEmpty(PreviousText) && ActivePage > 1)
{
writer.Write(" ");
writer.WriteBeginTag("a");
string pageUrl = StringUtils.SetUrlEncodedKey(BaseUrl, QueryStringPageField, (ActivePage - 1).ToString());
writer.WriteAttribute("href", pageUrl);
if (!string.IsNullOrEmpty(PageLinkCssClass))
writer.WriteAttribute("class", PageLinkCssClass + " " + PageLinkCssClass + "-prev");
writer.Write(HtmlTextWriter.SelfClosingTagEnd);
writer.Write(PreviousText);
writer.WriteEndTag("a");
}
// Next link
if (ShowPreviousNextLinks && !string.IsNullOrEmpty(NextText) && ActivePage < TotalPages)
{
writer.Write(" ");
writer.WriteBeginTag("a");
string pageUrl = StringUtils.SetUrlEncodedKey(BaseUrl, QueryStringPageField, (ActivePage + 1).ToString());
writer.WriteAttribute("href", pageUrl);
if (!string.IsNullOrEmpty(PageLinkCssClass))
writer.WriteAttribute("class", PageLinkCssClass + " " + PageLinkCssClass + "-next");
writer.Write(HtmlTextWriter.SelfClosingTagEnd);
writer.Write(NextText);
writer.WriteEndTag("a");
}
writer.WriteEndTag("div");
if (RenderContainerDiv)
{
if (RenderContainerDivBreak) writer.Write("<br clear=\"all\" />\r\n");
writer.WriteEndTag("div");
}
}
As I said pretty much brute force rendering based on
the control’s property settings of which there are quite a few:
You can also see
the pager in
the designer above. unfortunately
the VS designer (both 2010 and 2008) fails to render
the float: left CSS styles properly and starts wrapping after margins are applied in
the special buttons. Not a big deal since VS does at least respect
the spacing (the floated elements overlay). Then again I’m not using
the designer anyway :-}.
Filtering Data
What makes
the Pager easy to use is
the filter methods built into
the control. While this functionality is clearly not
the most politically correct design choice as it violates separation of concerns, it’s very useful for typical pager operation. While I actually have filter methods that do something similar in my business layer, having it exposed on
the control makes
the control a lot more useful for typical databinding scenarios. Of course these methods are optional – if you have a business layer that can provide filtered page queries for you can use that instead and assign
the TotalItems property manually.
There are three filter method types available for IQueryable, IEnumerable and for DataTable which tend to be
the most common use cases in my apps old and new.
The IQueryable version is pretty simple as it can simply rely on on .Skip() and .Take() with LINQ:
/// <summary>
/// <summary>
/// Queries
the database for
the ActivePage applied manually
/// or from
the Request["page"] variable. This routine
/// figures out and sets TotalPages, ActivePage and
/// returns a filtered subset IQueryable that contains
/// only
the items from
the ActivePage.
/// </summary>
/// <param name="query"></param>
/// <param name="activePage">
///
The page you want to display. Sets
the ActivePage property when passed.
/// Pass 0 or smaller to use ActivePage setting.
/// </param>
/// <returns></returns>
public IQueryable<T> FilterIQueryable<T>(IQueryable<T> query, int activePage)
where T : class, new()
{
ActivePage = activePage < 1 ? ActivePage : activePage;
if (ActivePage < 1)
ActivePage = 1;
TotalItems = query.Count();
if (TotalItems <= PageSize)
{
ActivePage = 1;
TotalPages = 1;
return query;
}
int skip = ActivePage - 1;
if (skip > 0)
query = query.Skip(skip * PageSize);
_TotalPages = CalculateTotalPagesFromTotalItems();
return query.Take(PageSize);
}
The IEnumerable<T> version simply converts
the IEnumerable to an IQuerable and calls back into this method for filtering.
The DataTable version requires a
little more work to manually parse and filter records (I didn’t want to add
the Linq DataSetExtensions assembly just for this):
/// <summary>
/// Filters a data table for an ActivePage.
///
/// Note: Modifies
the data set permanently by remove DataRows
/// </summary>
/// <param name="dt">Full result DataTable</param>
/// <param name="activePage">Page to display. 0 to use ActivePage property </param>
/// <returns></returns>
public DataTable FilterDataTable(DataTable dt, int activePage)
{
ActivePage = activePage < 1 ? ActivePage : activePage;
if (ActivePage < 1)
ActivePage = 1;
TotalItems = dt.Rows.Count;
if (TotalItems <= PageSize)
{
ActivePage = 1;
TotalPages = 1;
return dt;
}
int skip = ActivePage - 1;
if (skip > 0)
{
for (int i = 0; i < skip * PageSize; i++ )
dt.Rows.RemoveAt(0);
}
while(dt.Rows.Count > PageSize)
dt.Rows.RemoveAt(PageSize);
return dt;
}
Using
the Pager Control
The pager as it is is a first cut I built a couple of weeks ago and since then have been tweaking a
little as part of an internal project I’m working on. I’ve replaced a bunch of pagers on various older pages with this pager without any issues and have what now feels like a more consistent user interface where paging looks and feels
the same across different controls. As a bonus I’m only loading
the data from
the database that I need to display a single page. With
the preset class tags applied too adding a pager is now as easy as dropping
the control and adding
the style sheet for styling to be consistent – no fuss, no muss. Schweet.
Hopefully some of you may find this as useful as I have or at least as a baseline to build ontop of…
Resources
The Pager is part of
the West Wind Web & Ajax Toolkit
Pager.cs Source Code (some toolkit dependencies)
Westwind.css base stylesheet with .pager and .gridpager styles
Pager Example Page
© Rick Strahl, West Wind Technologies, 2005-2010Posted in ASP.NET
