Build Your Own ASP.NET 3.5 Website Using C# & VB (25 page)

content from an XML file, the administration and updating of banner advertisement

files and their properties is a snap. Also, the XML file allows you to control the

banner’s image, link, link target, and frequency of appearance in relation to other

banner ads.

The benefits of using this control don’t stop there, though. Most of the AdRotator

control’s properties reside within an XML file, so, if you wanted to, you could share

that XML file on the Web, allowing value added resellers (VARS), or possibly your

companies’ partners, to use your banner advertisements on their web sites.

What Is XML?

In essence, XML is simply a text-based format for the transfer or storage of data;

it contains no details about how that data should be presented. XML is very easy

to start with because of its close resemblance to your old friend HTML: both are

largely comprised of tags inside angle brackets (< and >), and any tag may contain

attributes that are specific to that tag. The biggest difference between XML and

HTML is that, rather than providing a fixed set of tags as HTML does, XML allows

us to create our own tags to describe the data we wish to represent.

Take a look at the following HTML element:

Star Wars Episode I: The Phantom Menace

This example describes the content between the tags as a level one heading. This

is fine if all we want to do is display the heading “Star Wars Episode I: The

Phantom Menace” on a web page. But what if we want to access those words as

data?

Like HTML, XML’s purpose is to describe the content of a document. But where

HTML is a very generic markup language for documents—headings, paragraphs

and lists, for example—XML can, very specifically, describe
what the content is
.

Using XML, the web author can mark up the contents of a document, describing

that content in terms of its relevance as data.

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We can use XML to mark up the words “Star Wars Episode I: The Phantom Menace” in a way that better reflects this content’s significance as data:

Here, the XML tag names we’ve chosen best describe the contents of the element.

We also define our own attribute names as necessary. For instance, in the example

above, you may decide that you want to differentiate between the VHS version

and the DVD version of the film, or record the name of the movie’s director. This

can be achieved by adding attributes and elements, as shown below:

format="DVD"
>

George Lucas

If you want to test this control out, create a file called
ads.xml
in your
LearningASP\VB

or
LearningASP\CS
folder (or both), and insert the content presented below. Feel free

to create your own banners, or to use those provided in the code archive for this

book:

LearningASP\VB\Ads.xml

workatdorknozzle.gif

http://www.example.com

_blank

Work at Dorknozzle!

HR Sites

2

getthenewsletter.gif

http://www.example.com

_blank

Get the Nozzle Newsletter!

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Marketing Sites

1

As you can see, the Advertisements element is the root node, and in accordance

with the XML specification, it appears only once. For each individual advertisement,

we simply add an Ad child element. For instance, the above advertisement file

contains details for two banner advertisements.

As you’ve probably noticed by now, the
.xml
file enables you to specify properties

for each banner advertisement by inserting appropriate elements inside each of the

Ad elements. These elements include:

ImageURL

the URL of the image to display for the banner ad

NavigateURL

the web page to which your users will navigate when they click the banner ad

AlternateText

the alternative text to display for browsers that don’t support images

Keyword

the keyword to use to categorize your banner ad

If you use the KeywordFilter property of the AdRotator control, you can specify

the categories of banner ads to display.

Impressions

the relative frequency with which a particular banner ad should be shown in

relation to other banner advertisements

The higher this number, the more frequently that specific banner will display

in the browser. The number provided for this element can be as low as one, but

cannot exceed 2,048,000,000; if it does, the page throws an exception.

Except for ImageURL, all these elements are optional. Also, if you specify an Ad

without a NavigateURL, the banner ad will display without a hyperlink.

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To make use of this
Ads.xml
file, create a new ASP.NET page called
AdRotator.aspx
, and add the following code to it:

Visual Basic

LearningASP\VB\AdRotator.aspx

<%@ Page Language="VB" %>

"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

Figure 4.6. Displaying ads using
AdRotator.aspx

As with most of our examples, the C# version of this code is the same except for

the Page declaration. You’ll also need to copy the
workatdorknozzle.gif
and
getthe-
newsletter.gif
image files from the code archive and place them in your working

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Constructing ASP.NET Web Pages

127

folder in order to see these ad images. Save your work and test it in the browser;

the display should look something like
Figure 4.6.

Refresh the page a few times, and you’ll notice that the first banner appears more

often than the second. This occurs because the Impression value for the first Ad is

double the value set for the second banner, so it will appear twice as often.

TreeView

The TreeView control is a very powerful control that’s capable of displaying a

complex hierarchical structure of items. Typically, we’d use it to view a directory

structure or a site navigation hierarchy, but it could be used to display a family tree,

a corporate organizational structure, or any other hierarchical structure.

The TreeView can pull its data from various sources. We’ll talk more about the

various kinds of data sources later in the book; here, we’ll focus on the

SiteMapDataSource class, which, as its name suggests, contains a hierarchical

sitemap. By default, this sitemap is read from a file called
Web.sitemap
that’s located in the root of your project (you can easily create this file using the
Site Map
template in Visual Web Developer).
Web.sitemap
is an XML file that looks like this:

LearningASP\VB\Web.sitemap

xmlns="http://schemas.microsoft.com/AspNet/SiteMap-File-1.0">

description="Home">

description="TreeView Example" />

description="TreeView Example" />

description="ClickEvent Example" />

description="Loops Example" />

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A Web.sitemap Limitation

An important limitation to note when you’re working with
Web.sitemap
files is

that they must contain only one siteMapNode as the direct child of the root

siteMap element.

In the example above, the siteMapNode with the title Home is this single

siteMapNode. If we added another siteMapNode alongside (rather than inside)

this element, the
Web.sitemap
file would no longer be valid.

To use this file, you’ll need to add a SiteMapDataSource control to the page, as well

as a TreeView control that uses this data source, like this:

Visual Basic

LearningASP\VB\TreeViewSiteMap.aspx

<%@ Page Language="VB" %>

"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

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