Developing Dynamic WAP Applications

In the second part of this paper, I shall discuss some of the issues involving in developing dynamic WAP applications:

 

Ø       Redirecting pages

Ø       Caching on WAP devices

Ø       Cookie support on WAP devices, and maintaining state using the ASP Session object

Ø       Maintaining state without cookie support

Ø       Detecting WAP devices

Ø       Passing values from ASP server-side variables to WML client-side variables, and vice versa.

Ø       Tips for using ASP to generate WML content

Ø       Common errors

Redirecting Pages

In web application development, it's not unusual to see a browser being redirected to another web page. This may happen, for example, because you don't have the permissions required to view a page, and you must therefore log in before you can do so.

 

In ASP, you can use the Response.Redirect() method to perform page redirection. Let's take a look at an example.

Deck1.asp

<% Response.ContentType = "text/vnd.wap.wml" %>

<% Response.Buffer = True %>

<?xml version="1.0"?>

<!DOCTYPE wml PUBLIC "-//WAPFORUM//DTD WML 1.1//EN"

                     "http://www.wapforum.org/DTD/wml_1.1.xml">

<wml>

   <card id="card1deck1" title="Deck1">

      <p>

         This is card 1, but you won't see it...

         <% Response.Redirect "deck2.asp" %>

      </p>

   </card>

</wml>

Deck2.asp

<% Response.ContentType = "text/vnd.wap.wml" %>

<?xml version="1.0"?>

<!DOCTYPE wml PUBLIC "-//WAPFORUM//DTD WML 1.1//EN"

                     "http://www.wapforum.org/DTD/wml_1.1.xml">

<wml>

   <card id="card1deck2" title="Deck2">

      <p>

         This is deck2.

      </p>

   </card>

</wml>

 

When deck1 is viewed using the UP.Simulator, the WAP browser will be redirected to deck2.

 

 

Note that for redirection to occur, you must buffer the page created by the ASP parser using the Response.Buffer property:

 

<% Response.Buffer = True %>

If a page is not buffered, the web server will send the HTTP headers to the client before the ASP parser has finished parsing the ASP document. In the case of page redirection, this will cause an error. Try setting the Response.Buffer property to False, and you'll see the error message:

 

 

The error message is:

 

The HTTP headers are already written to the client browser. Any HTTP header modifications must be made before writing page content.