Webmaster''''s Guide to the Wireless Internet part 20 pptx

Using WMLScript and Microsoft Active Server Pages ASP: Case Study We have seen how WMLScript can be used to perform client-side validation and to complement WML applications that run on

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Using WMLScript and Microsoft Active Server Pages (ASP): Case Study

We have seen how WMLScript can be used to perform client-side validation and

to complement WML applications that run on a WAP device One particular appli-cation that is very popular is a currency converter However, the conventional cur-rency converter usually hardcodes the exchange rate in the WMLScript program Once the WMLScript is downloaded onto the device, it is cached and any changes

to the currency conversion rate would not be reflected in the application

In this case study, we will illustrate how you can use ASP to create a truly dynamic WMLScript program using the currency converter application as a case study Our currency converter is able to reflect the daily changes in the exchange rates

Designing the Application

A currency converter application often is used to illustrate the use of WMLScript For this example, we will use the UP.Simulator provided by Openwave Figure 4.16 and Figure 4.17 illustrate the desired outcome of our application

www.syngress.com

Figure 4.16Selecting the USD Option to Convert from, and Keying the Amount to Convert

Figure 4.17Selecting the SIN Option to Convert to, and Viewing the Result

of the Conversion

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The user simply chooses the currency to convert from, keys in the amount to

be converted, and selects the target currency.The converted currency would then

be displayed

Creating the Database Our application makes use of a database containing a single table named

Conversion.The database table can be seen in Figure 4.18

This table simply contains the exchange rate of currencies.The exchange rate

is tagged to a fixed currency, the Singapore dollar in this case For example:

1 USD (US Dollar) = 1.73 SIN (Singapore Dollar)

1 RM (Malaysian Ringgit)= 0.48 SIN

Converting from one currency to another is a two-step process For example:

1 To convert 15 USD to RM, first convert the USD to SIN:

15 * 1.73 = 25.95 SIN

2 Then convert the SIN to RM:

25.95 / 0.48 = 54.0625 RM

The Conversion table contains two fields: Currency and SinEquiv.The Currency field contains the currency name and the SinEquiv field contains the equivalent amount of the currency in Singapore dollar

The WML Deck Let’s take a look at the WML deck that loads the application.The code can be seen in Figure 4.19

www.syngress.com Figure 4.18Our Database Contains One Table Named Conversion

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Figure 4.19Currency.wml

<?xml version="1.0"?>

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

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

<wml>

<p>

Currency to convert from:

</select>

Enter Currency: <input type="text" name="amount" format="*N"/> Currency to convert to:

</select>

</do>

</p>

</card>

<p>

Please select a different currency.

</p>

</card>

</wml>

There are two cards within the deck.The first card takes care of user input, and once the user is done with it, links to the WMLScript:

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Notice that we did not link to a WMLScript file with the wmls file exten-sion Instead, we have pointed the deck to an ASP file.We are going to use Microsoft Active Server Pages to dynamically generate the WMLScript program

The amount to be converted is also passed as an input parameter to the function

named Convert().

Generating the WMLScript Program from ASP

In the early days of the Web, most of the pages were static—content remains the same unless it was changed by a webmaster or a Web designer However, with the explosive growth of the Internet (and the World Wide Web), people have realized the importance and necessity of dynamic content And very soon after, different technologies were developed to enable Web sites to publish content that was dynamic, through the use of server-side technologies A good example would be CGI scripts that return stock pages when requested.These pages often contain information stored in a database Some of the other server-side

technologies/products include:

■ Microsoft Active Server Pages (ASP)

■ Java Server Pages (JSP)

■ ColdFusion Application Server

■ PHP Hypertext Preprocessor (PHP)

In this example, we will illustrate server-side processing using Microsoft ASP

Readers who are not familiar with ASP could refer to the following sources for learning ASP:

■ www.w3schools.com/asp/default.asp

■ www.learnasp.com The listing in Figure 4.20 shows the ASP document generating the WMLScript program

Figure 4.20Calculate.asp

<!—#INCLUDE file="adovbs.inc" —>

<%

Response.ContentType="text/vnd.wap.wmlscript"

if hour(time())>=0 AND minute(time())>=00 AND hour(time())<8 AND minute(time())<=59 then

Continued

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Response.ExpiresAbsolute = MonthName( month(date()) , true) &

" " & day(date()) & " 8:00:00"

else Response.ExpiresAbsolute = MonthName( month(date()+1) , true)

& " " & day(date() + 1) & " 8:00:00"

end if

%>

extern function Convert(amount){

var origAmt=amount;

var fromCurrency = WMLBrowser.getVar("fromCurrency");

var toCurrency = WMLBrowser.getVar("toCurrency");

if (String.compare(fromCurrency,toCurrency)==0) { WMLBrowser.go("currency.wml#card2");

return;

}

<%

Dim rs Set rs = Server.CreateObject("ADODB.Recordset") connStr = "DRIVER={Microsoft Access Driver (*.mdb)};DBQ=" &

Server.MapPath("currency.mdb") & ";"

rs.Open "Conversion", connStr, adOpenKeySet, adLockOptimistic

%>

var USD =<% rs.Find "Currency = 'USD'"

response.write rs("SinEquiv")

%>;

var SIN =<% rs.MoveFirst

rs.Find "Currency = 'SIN'"

%>;

var RM = <% rs.MoveFirst

rs.Find "Currency = 'RM'"

%>;

if (fromCurrency=="USD") {

Figure 4.20Continued

Continued

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amount = USD * amount;

} else if (fromCurrency=="RM") { amount = RM * amount;

}

if (toCurrency=="USD") { amount = amount / USD;

} else if (toCurrency=="RM") { amount = amount / RM;

} amount *=1.0;

var str = origAmt + " " + fromCurrency + " is " ; Dialogs.alert(str + String.format("%.2f",amount) + " " + toCurrency);

}

We use ASP to dynamically generate the WMLScript program.The reason for this is that we want to load the currency exchange rate from a database so that it

is always current By doing that, the user is always using the latest exchange rate for conversion

However, there is a little problem is doing this As database access is required,

it could be a time-consuming affair if we generate the WMLScript program every time someone needs to use the application In a Web environment where concurrency is an important factor in determining the success of your site, this problem is going to drastically slow down your server

Fortunately, the nature of this application does not require that the user require up-to-the-minute exchange rates It would be reasonable if the exchange rates were updated once a day

To solve this problem, we make use of the caching property of WMLScript on the device.What we could do is to set the expiration date of the WMLScript to every morning at 8:00 A.M.When a user accesses the application after 8:00 A.M., or loads the application for the first time, the WMLScript is fetched from the server and cached for later use Subsequent usage would then be loaded from the cache

www.syngress.com Figure 4.20Continued

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Let’s now take a closer look at our WMLScript file:

<!—#INCLUDE file="adovbs.inc" —>

Since we are using ActiveX Data Objects (ADO) for database access, we need

to include the adovbs.inc file containing all the ADO constants used by VBScript

<%

Response.ContentType="text/vnd.wap.wmlscript"

Remember that since we are generating the WMLScript file dynamically, we need to explicitly set the MIME type in the ASP document using the

Response.ContentType property Note that a pair of <% %> tags encloses the ASP codes (VBScript in this case)

if hour(time())>=0 AND minute(time())>=00 AND hour(time())<8 AND minute (time())<=59 then

Response.ExpiresAbsolute = MonthName( month(date()) , true) & " " & day(date()) & " 8:00:00"

else

Response.ExpiresAbsolute = MonthName( month(date()+1) , true) & " "

& day(date() + 1) & " 8:00:00"

end if

The next portion of the code determines the expiration date of the WMLScript.The checking is simple: if the user loads the ASP document after 12 midnight, the expiration date would be set to 8:00 A.M the same day If the ASP document is loaded after 8:00 A.M., the expiration date would then be set to 8:00

A.M the next day.To set the expiration date, use the Response.ExpiresAbsolute property.The date format looks like this: “Oct 21 8:00:00”

function Convert(amount){

var origAmt=amount;

var fromCurrency = WMLBrowser.getVar("fromCurrency");

var toCurrency = WMLBrowser.getVar("toCurrency");

Next we have the Convert() function For a WMLScript function to be

callable from WML, it needs to have the extern keyword.Within the function we defined three variables using the var keyword.The first variable is used to store

the original amount to be converted, and the next two variables retrieve the two currencies involved in the conversion In order for WMLScript to interact with WML, you can use the WMLBrowser library.There are a number of functions

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within the library that allow you to communicate with the WML deck.The

getVar()function retrieves the values of WML variables

Before we start the conversion, we want to make sure that the two currencies

involved are not identical For string comparisons, use the compare() function

from the String library If they are identical, load the second card in the WML

deck and exit the WMLScript function using the return keyword.

if (String.compare(fromCurrency,toCurrency)==0) { WMLBrowser.go("currency.wml#card2");

return;

} Because we are getting the conversion rates from a database, we need to use ADO for data access

<%

Dim rs Set rs = Server.CreateObject("ADODB.Recordset") connStr = "DRIVER={Microsoft Access Driver (*.mdb)};DBQ=" &

Server.MapPath("currency.mdb") & ";"

%>

Once the records in the database are retrieved, we proceed to assign the indi-vidual rate to the respective variables

%>;

var SIN =<% rs.MoveFirst

rs.Find "Currency = 'SIN'"

%>;

var RM = <% rs.MoveFirst

rs.Find "Currency = 'RM'"

%>;

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The Find() method of the Recordset object is used to locate the correct

record to assign to the variables Note that after the first variable is assigned, you

need to perform a MoveFirst() operation so as to ensure that the search always

begin from the first record Also, recall earlier that we opened the recordset using

the adOpenKeyset cursor:

This is important because using the default cursor (adOpenForwardOnly)

will cause the MoveFirst() method to fail Finally, we perform the conversion:

if (fromCurrency=="USD") {

amount = USD * amount;

} else if (fromCurrency=="RM") {

amount = RM * amount;

}

if (toCurrency=="USD") {

amount = amount / USD;

} else if (toCurrency=="RM") {

amount = amount / RM;

}

The result is then displayed using the alert() function from the Dialogs

library

amount *= 1.0;

var str = origAmt + " " + fromCurrency + " is " ;

Dialogs.alert(str + String.format("%.2f",amount) + " " + toCurrency); }

The format() function from the String library formats the result to two

decimal places

Debugging the WMLScript

One of the difficulties that we found when coding this application is deciding how to troubleshoot your WMLScript when you are faced with problems Since

we are using the UP.Simulator for this application, we naturally turn to the Phone Information window for help when it comes to debugging

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Apart from some of the syntax errors that would quite often emerge, another tricky problem is with caching.You need to ensure that the WMLScript file is cached and used at the right time

Let’s discuss the first problem, syntax error Syntax error can be detected easily using the Phone Information window For example, assume we have the fol-lowing error in our WMLScript program:

%> // missing ";"

This error will generate an error in the compilation process, and the deck shown in Figure 4.21 would be displayed

Looking into the Phone Information window (see Figure 4.22) reveals the following source of error

(25) : error: syntax error at "var" missing ;

www.syngress.com Figure 4.21The UP.Simulator Displaying an Error Message

Figure 4.22Looking into the Phone Information Window for Sources of Error

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