C# 4 and .NET 4

outing ❘ 1245
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Defining routes — ASP.NET routing requires you to define the routes that are available in your web
site so that they can be used.
Using route parameters — Once a route has been detected in a URL, the target page can make use of
routing parameters.
The downloadable code for this chapter includes a simple solution called PCSRoutingDemo that will be
referred to from this section to illustrate the techniques.
query string Parameters
While surfing the web, you’ve probably noticed that a lot of web pages include information in their URLs in
addition to their location. For example, in an e-commerce web site, you might see a URL that looks a little
like the following:
http://www.myecommercesite.com/products.aspxid=4
In this URL the target page is products.aspx, but after the identifier for this page, you can see additional
information in the form of a query string. The character indicates the start of the query string, and the
remainder of the URL consists of a name/value pair, with an equals character (=) separating the name (id)
from the value (4). In fact, URLs can contain several query string name/value pairs, separated by & symbols.
When users navigate to an ASP.NET page with a query string (perhaps by clicking on a link that you have
rendered from database data), you can write code to render the page accordingly. In this example, you
might use the value of the id query string parameter to extract data from a database, for a product with the
corresponding ID. This means that you don’t have to create a page for every product in your database; you
can, instead, create a single page that can show the details for any product.
In practice, ASP.NET pages receive query string information in the form of a NameValueCollection object.
This is passed in the QueryString property of the HttpRequest object that is available in code-behind
through the inherited Request property. The query string collection is indexed by name and index, so to get
the value of the id query string parameter shown above, you could use either of the following lines of code:
or:
string idValue = Request.QueryString[0];
string idValue = Request.QueryString["id"];
Note that all query string values are passed as strings, so to get an integer value for id you’d need to parse
the value.
The use of query string parameters is illustrated in the PCSRoutingDemo web site for this chapter. If you
view the web site in a browser and click the “Navigation with query string” link, you will see the query
string parameters displayed, as shown in Figure 42-1.
figure 42-1
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