WML-Tutorial

WML Tutorial M.Sc. IT Course Code: PS03CINT02

WML Tutorial
WML is an XML language used to specify content and user interface
for WAP devices like PDA and Mobile Phones.

The WAP forum provides a DTD for WML.

This tutorial gives you complete understanding on WML language
to develop WAP applications.

WML - Overview

The topmost layer in the WAP (Wireless Application Protocol) architecture is made up of
WAE (Wireless Application Environment), which consists of WML and WML scripting
language.

WML stands for Wireless Markup Language
WML is an application of XML, which is defined in a document-type definition.
WML is based on HDML and is modified so that it can be compared with HTML.
WML takes care of the small screen and the low bandwidth of transmission.
WML is the markup language defined in the WAP specification.
WAP sites are written in WML, while web sites are written in HTML.
WML is very similar to HTML. Both of them use tags and are written in plain text
format.
WML files have the extension ".wml". The MIME type of WML is
"text/vnd.wap.wml".
WML supports client-side scripting. The scripting language supported is called
WMLScript.

WML Versions:

WAP Forum has released a latest version WAP 2.0. The markup language defined in WAP
2.0 is XHTML Mobile Profile (MP). The WML MP is a subset of the XHTML. A style sheet
called WCSS (WAP CSS) has been introduced alongwith XHTML MP. The WCSS is a
subset of the CSS2.

Most of the new mobile phone models released are WAP 2.0-enabled. Because WAP 2.0 is
backward compatible to WAP 1.x, WAP 2.0-enabled mobile devices can display both
XHTML MP and WML documents.

WML 1.x is an earlier technology. However, that does not mean it is of no use, since a lot
of wireless devices that only supports WML 1.x are still being used. Latest version of
WML is 2.0 and it is created for backward compatibility purposes. So WAP site
developers need not to worry about WML 2.0.

WML Decks and Cards:

Mr. Pritesh N. Patel ISTAR Page 1


A main difference between HTML and WML is that the basic unit of navigation in HTML
is a page, while that in WML is a card. A WML file can contain multiple cards and they
form a deck.

When a WML page is accessed from a mobile phone, all the cards in the page are
downloaded from the WAP server. So if the user goes to another card of the same deck,
the mobile browser does not have to send any requests to the server since the file that
contains the deck is already stored in the wireless device.

You can put links, text, images, input fields, option boxes and many other elements in a
card.

WML Program Structure:

Following is the basic structure of a WML program:

<?xml version="1.0"?>
<!DOCTYPE wml PUBLIC "-//WAPFORUM//DTD WML 1.2//EN"
"http://www.wapforum.org/DTD/wml12.dtd">

<wml>

<card id="one" title="First Card">
<p>
This is the first card in the deck
</p>
</card>

<card id="two" title="Second Card">
<p>
Ths is the second card in the deck
</p>
</card>

</wml>

The first line of this text says that this is an XML document and the version is 1.0. The
second line selects the document type and gives the URL of the document type definition
(DTD).

One WML deck (i.e. page ) can have one or more cards as shown above. We will see
complete detail on WML document structure in subsequent chapter.

Unlike HTML 4.01 Transitional, text cannot be enclosed directly in the <card>...</card>
tag pair. So you need to put a content inside <p>...</p> as shown above.

WAP Site Design Considerations:



Wireless devices are limited by the size of their displays and keypads. It's therefore very
important to take this into account when designing a WAP Site.

While designing a WAP site you must ensure that you keep things simple and easy to
use. You should always keep in mind that there are no standard microbrowser behaviors
and that the data link may be relatively slow, at around 10Kbps. However, with GPRS,
EDGE, and UMTS, this may not be the case for long, depending on where you are
located.

The following are general design tips that you should keep in mind when designing a
service:

Keep the WML decks and images to less than 1.5KB.
Keep text brief and meaningful, and as far as possible try to precode options to
minimize the rather painful experience of user data entry.
Keep URLs brief and easy to recall.
Minimize menu levels to prevent users from getting lost and the system from
slowing down.
Use standard layout tags such as <big> and <b>, and logically structure your
information.
Don't go overboard with the use of graphics, as many target devices may not
support them.

WML - Environment

To develop WAP applications you will need the following:

A WAP enabled Web Server: You can enable your Apache or Microsoft IIS to serve
all the WAP client request.
A WAP Gateway Simulator This is required to interact to your WAP server.
A WAP Phone Simulator: This is required to test your WAP Pages and to show all
the WAP pages.

You can write your WAP pages using following languages:

Wireless Markup Language(WML) to develop WAP application.
WML Script to enhance the functionality of WAP application.

Configuring Web Server:

In normal web applications, MIME type is set to text/html, designating normal HTML
code. Images, on the other hand, could be specified as image/gif or image/jpeg, for
instance. With this content type specification, the web browser knows the data type that
the web server returns.

To make your Apache WAP compatible you have nothing to do very much. You simply
need to add support for the MIME types and extensions listed below.



File Extension MIME type

WML (.wml) text/vnd.wap.wml

WMLScript (.wmls) text/vmd.wap.wmlscript

WMLScriptc (.wmlsx) application/vnd.wap.wmlscriptc

WMLC (.wmlc) application/vnd.wap.wmlc

WBMP (.wbmp) image/vnd.wap.wbmp

Configure Apache Web Server for WAP:

Assuming you have Apache Web server installed on your machine. So now we will tell
you how to enable WAP functionality in your Apache web server.

So locate Apache's file httpd.conf which is usually in /etc/httpd/conf, and add the
following lines to the file and restart the server:

AddType text/vnd.wap.wml .wml
AddType text/vnd.wap.wmlscript .wmls
AddType application/vnd.wap.wmlc .wmlc
AddType application/vnd.wap.wmlscriptc .wmlsc
AddType image/vnd.wap.wbmp .wbmp

In dynamic applications, the MIME type must be set on the fly, whereas in static WAP
applications the web server must be configured appropriately.

Configure Microsoft IIS for WAP:

To configure a Microsoft IIS server to deliver WAP content, you need to perform the
following:

1. Open the Internet Service Manager console and expand the tree to view your Web
site entry. You can add the WAP MIME types to a whole server or individual
directories.
2. Open the Properties dialog box by right-clicking the appropriate server or
directory, then choose Properties from the menu.
3. From the Properties dialog, choose the HTTP Headers tab, then select the File
Types button at the bottom right.
4. For each MIME type listed earlier in the above table, supply the extension with or
without the dot (it will be automatically added for you), then click OK in the
Properties dialog box to accept your changes.



Installing WAP Gateway Simulator:

There are many WAP Gateway Simulator available on the Internet so download any of
them and install on your PC. You would need to run this gateway before starting WAP
Mobile simulator.

WAP Gateway will take your request and will pass it to the Web Server and whatever
response will be received from the Web server that will be passed to the Mobile
Simulator.

You can download it from Nokia web site:

Nokia WAP Gateway simulator - Download Nokia WAP Gateway simulator.

Installing WAP Phone Simulator:

There are many WAP Simulator available on the Internet so download any of them and
install on your PC which you will use as a WAP client. Here are popular links to
download simulator:

Nokia WAP simulator - Download Nokia WAP simulator.
WinWAP simulator - Download WinWAP browser from their official website.

NOTE: If you have WAP enabled phone then you do not need to install this simulator.
But while doing development it is more convenient and economic to use a simulator.

The WAP Model:

I am giving this section just for your reference, if you are not interested then you can
skip this section.

The figure below shows the WAP programming model. Note the similarities with the
Internet model. Without the WAP Gateway/Proxy the two models would have been
practically identical.



WAP Gateway/Proxy is the entity that connects the wireless domain with the Internet.
You should make a note that the request that is sent from the wireless client to the WAP
Gateway/Proxy uses the Wireless Session Protocol (WSP). In its essence, WSP is a binary
version of HTTP.

A markup language - the Wireless Markup Language (WML) has been adapted to develop
optimized WAP applications. In order to save valuable bandwidth in the wireless
network, WML can be encoded into a compact binary format. Encoding WML is one of
the tasks performed by the WAP Gateway/Proxy.

How WAP Model Works?

When it comes to actual use, WAP works like this:

1. The user selects an option on their mobile device that has a URL with Wireless
Markup language (WML) content assigned to it.
2. The phone sends the URL request via the phone network to a WAP gateway, using
the binary encoded WAP protocol.
3. The gateway translates this WAP request into a conventional HTTP request for the
specified URL, and sends it on to the Internet.
4. The appropriate Web server picks up the HTTP request.
5. The server processes the request, just as it would any other request. If the URL
refers to a static WML file, the server delivers it. If a CGI script is requested, it is
processed and the content returned as usual.
6. The Web server adds the HTTP header to the WML content and returns it to the
gateway.



7. The WAP gateway compiles the WML into binary form.
8. The gateway then sends the WML response back to the phone.
9. The phone receives the WML via the WAP protocol.
10. The micro-browser processes the WML and displays the content on the
screen.

WML - Syntax

A WML program is typically divided into two parts: the document prolog and the body.
Consider the following code:

Following is the basic structure of a WML program:


<wml>

<card id="one" title="First Card">
<p>
This is the first card in the deck

</p>
</card>

<card id="two" title="Second Card">
<p>
Ths is the second card in the deck
</p>
</card>

</wml>

WML Document Prolog:

The first line of this text says that this is an XML document and the version is 1.0. The
second line selects the document type and gives the URL of the document type definition
(DTD). The DTD referenced is defined in WAP 1.2, but this header changes with the
versions of the WML. The header must be copied exactly so that the tool kits
automatically generate this prolog.

The prolog components are not WML elements and they should not be closed, i.e. you
should not give them an end tag or finish them with />.



WML Document Body:

The body is enclosed within a <wml> </wml> tag pair. The body of a WML document can
consist of one or more of the following:

Deck
Card
Content to be shown
Navigation instructions

Unlike HTML 4.01 Transitional, text cannot be enclosed directly in the <card>...</card>
tag pair. So you need to put a content inside <p>...</p> as shown above.

Testing Your Program:

Put above code in a file called test.wml file, and put this WML file locally on your hard
disk, then view it using an emulator.

This is by far the most efficient way of developing and testing WML files. Since your aim
is, however, to develop a service that is going to be available to WAP phone users, you
should upload your WML files onto a server once you have developed them locally and
test them over a real Internet connection. As you start developing more complex WAP
services, this is how you will identify and rectify performance problems, which could, if
left alone, lose your site visitors.

In uploading the file test.wml to a server, you will be testing your WML emulator to see
how it looks and behaves, and checking your Web server to see that it is set up correctly.
Now start your emulator and use it to access the URL of test.wml. For example, the URL
might look something like this:

http://websitename.com/wapstuff/test.wml

NOTE: Before accessing any URL, make sure WAP Gateway Simulator is running on
your PC.

When you will download your WAP program then you will see only first card at your
mobile. Following is the output of the above example on Nokia Mobile Browser 4.0. This
mobile supports horizontal scrolling. You can see the text off the screen by pressing the
"Left" or "Right" button.


When you press right button then second card will be visible as follows:

WML - Elements

WML is defined by a set of elements that specify all markup and structural information
for a WML deck. Elements are identified by tags, which are each enclosed in a pair of
angle brackets.

Unlike HTML, WML strictly adheres to the XML hierarchical structure, and thus,
elements must contain a start tag; any content such as text and/or other elements; and
an end tag. Elements have one of the following two structures:

<tag> content </tag> : This form is identical to HTML.
<tag />: This is used when an element cannot contain visible content or is empty,
such as a line break. WML document's prolog part does not have any element
which has closing element.

Following table lists the majority of valid elements. A complete detail of all these
elements is given in WML Tags Reference.

Deck & Card Elements
WML Elements Purpose
<!--> Defines a WML comment
<wml> Defines a WML deck (WML root)
<head> Defines head information
<meta> Defines meta information


<card> Defines a card in a deck
<access> Defines information about the access control of a
deck
<template> Defines a code template for all the cards in a deck

Text Elements
<br> Defines a line break
<p> Defines a paragraph
<table> Defines a table
<td> Defines a table cell (table data)
<tr> Defines a table row
<pre> Defines preformatted text

Text Formatting Tags
<b> Defines bold text
<big> Defines big text
<em> Defines emphasized text
<i> Defines italic text
<small> Defines small text
<strong> Defines strong text
<u> Defines underlined text

Image Elements
<img> Defines an image

Anchor Elements
<a> Defines an anchor
<anchor> Defines an anchor

Event Elements
<do> Defines a do event handler
<onevent> Defines an onevent event handler
<postfield> Defines a postfield event handler
<ontimer> Defines an ontimer event handler
<onenterforward> Defines an onenterforward handler
<onenterbackward> Defines an onenterbackward handler


<onpick> Defines an onpick event handler

Task Elements
<go> Represents the action of switching to a new card
<noop> Says that nothing should be done
<prev> Represents the action of going back to the previous
card
<refresh> Refreshes some specified card variables.

Input Elements
<input> Defines an input field
<select> Defines a select group
<option> Defines an option in a selectable list
<fieldset> Defines a set of input fields
<optgroup> Defines an option group in a selectable list

Variable Elements
<setvar> Defines and sets a variable
<timer> Defines a timer

WML - Comments

As with most programming languages, WML also provides a means of placing comment
text within the code.

Comments are used by developers as a means of documenting programming decisions
within the code to allow for easier code maintenance.

WML comments use the same format as HTML comments and use the following syntax:



A multiline comment can be given as follows:



The WML author can use comments anywhere, and they are not displayed to the user by
the user agent. Some emulators may complain if comments are placed before the XML
prolog.


Note that comments are not compiled or sent to the user agent, and thus have no effect
on the size of the compiled deck.

WML - Variables

Because multiple cards can be contained within one deck, some mechanism needs to be
in place to hold data as the user traverses from card to card. This mechanism is
provided via WML variables.

WML is case sensitive. No case folding is performed when parsing a WML deck. All
enumerated attribute values are case sensitive. For example, the following attribute
values are all different: id="Card1", id="card1", and id="CARD1".

Variables can be created and set using several different methods. Following are two
examples:

The <setvar> element:

The <setvar> element is used as a result of the user executing some task. The >setvar>
element can be used to set a variable's state within the following elements: <go>, <prev>,
and <refresh>.

This element supports the following attributes:

Attribute Value Description

name string Sets the name of the variable

value string Sets the value of the variable

class class data Sets a class name for the element.

id element ID A unique ID for the element.

The following element would create a variable named a with a value of 1000:
<setvar name="a" value="1000"/>

The input elements:

Variables are also set through any input element like input,select, option etc. A variable
is automatically created that corresponds with the named attribute of an input element.

For example , the following element would create a variable named b:

<select name="b">
<option value="value1">Option 1</option>
<option value="value2">Option 2</option>
</select>



Using Variables:

Variable expansion occurs at runtime, in the microbrowser or emulator. This means it
can be concatenated with or embedded in other text.

Variables are referenced with a preceding dollar sign, and any single dollar sign in your
WML deck is interpreted as a variable reference.

<p> Selected option value is $(b) </p>

WML - Formatting

This section will describe basic text formatting elements of WML.

Line Break:

The <br /> element defines a line break and almost all WAP browsers supports a line
break tag.

The <br /> element supports the following attributes:

xml:lang language_code Sets the language used in the element

Following is the example showing usage of <br /> element.


<wml>

<card title="Line Break Example">
<p align="center">
This is a <br /> paragraph with a line break.
</p>
</card>

</wml>

This will produce following result:



Text Paragraphs:

The <p> element defines a paragraph of text and WAP browsers always render a
paragraph in a new line.

A <p> element is required to define any text , image or a table in WML.

The <p> element supports the following attributes:

align left This is used to change the horizontal alignment
right of a paragraph.
center

mode wrap Sets whether a paragraph should wrap lines or
nowrap not.


Following is the example showing usage of <p> element.


<wml>

<card title="Paragraph Example">
<p align="center">
This is first paragraph
</p>
<p align="right">
This is second paragraph



</p>
</card>

</wml>


WML Tables:

The <table> element alongwith <tr> and <td> is used to create a table in WML. WML
does not allow the nesting of tables

A <table> element should be put with-in <p>...</p> elements.

The <table /> element supports the following attributes:

columns number Sets the number of columns in the table
align L To specify the horizontal text alignment of the
C columns, you need to assign three letters to the
R align attribute. Each letter represents the
horizontal text alignment of a column. The letter
can be L, C, or R. For example, if you want the
following settings to be applied to your table:

First table column -- Left-aligned
Second table column -- Center-aligned
Third table column -- Right-aligned

Then you should set the value of
the align attribute to LCR.



Following is the example showing usage of <table> element.


<wml>

<card title="WML Tables">
<p>
<table columns="3" align="LCR">
<tr>
<td>Col 1</td>
<td>Col 2</td>
<td>Col 3</td>
</tr>

<tr>
<td>A</td>
<td>B</td>
<td>C</td>
</tr>

<tr>
<td>D</td>
<td>E</td>
<td>F</td>
</tr>
</table>
</p>
</card>

</wml>


Preformatted Text:



The <pre> element is used to specify preformatted text in WML. Preformatted text is text
of which the format follows the way it is typed in the WML document.

This tag preserves all the white spaces enclosed inside this tag. Make sure you are not
putting this tag inside <p>...</p>

The <pre> element supports following attributes:


Following is the example showing usage of <pre> element.


<wml>

<card title="Preformatted Text">
<pre>
This is preformatted
text and will appear
as it it.
</pre>
</card>

</wml>


WML Fonts - <b>, <big>,<strong>,<italic>



WML does not support <font> element but there are other WML elements which you can
use to create different font effects like underlined text, bold text and italic text etc.

These tags are given in the following table:

<b> Defines bold text
<big> Defines big text
<em> Defines emphasized text
<i> Defines italic text
<small> Defines small text
<strong> Defines strong text
<u> Defines underlined text

These elements support the following attributes:


Following is the example showing usage of these elements.


<wml>

<card title="Text Formatting">
<p>
<b>bold text</b><br/>
<big>big text</big><br/>
<em>emphasized text</em><br/>
<i>italic text</i><br/>
<small>small text</small><br/>
<strong>strong text</strong><br/>
<u>underlined text</u>
</p>
</card>



</wml>


WML - Images

The <img> element is used to include an image in a WAP card. WAP-enabled wireless
devices only supported the Wireless Bitmap (WBMP) image format.

WBMP images can only contain two colors: black and white. The file extension of WBMP
is ".wbmp" and the MIME type of WBMP is "image/vnd.wap.wbmp".

The <img> element supports the following attributes:

align top Alignment the image
middle
bottom

alt alternative text Sets an alternate text to be displayed if the
image is not displayed.
height px Height of the image in poixels or percentage. If
% you specify the value in pixels, the syntax is
"140", instead of "140px".
hspace px Sets white space to the left and right of the
% image. If you specify the value in pixels, the
syntax is "140", instead of "140px".
localsrc cdata Sets an alternate representation for the image. If
this attribute is set, the browser will use it
instead of the "src" attribute.
src image url A path to wbmp image.
vspace px Sets white space above and below the image. If
% you specify the value in pixels, the syntax is
"140", instead of "140px".



width px Sets the width of the image.If you specify the
% value in pixels, the syntax is "140", instead of
"140px".

How to Make ".wbmp" Images

There are free tools available on the Internet to make ".wbmp" images.

The Nokia Mobile Internet Toolkit (NMIT) comes with a WBMP image editor that you can
use. You can convert existing GIF or JPG image files into WBMP file using NMIT.

Another free tool is ImageMagick, which can help you to create WBMP images.

Following is the example showing usage of <img> element.


<wml>

<card title="WML Images">
<p>
This is Thumb image
<img src="/images/thumb.wbmp" alt="Thumb Image"/>
</p>

<p>
This is Heart image
<img src="/images/heart.wbmp" alt="Heart Image"/>
</p>

</card>

</wml>




WML - Tables

The <table> element alongwith <tr> and <td> is used to create a table in WML. WML
does not allow the nesting of tables

A <table> element should be put with-in <p>...</p> elements.

The <table /> element supports the following attributes:

columns number Sets the number of columns in the table
align L To specify the horizontal text alignment of the
C columns, you need to assign three letters to the
R align attribute. Each letter represents the
horizontal text alignment of a column. The letter
can be L, C, or R. For example, if you want the
following settings to be applied to your table:

First table column -- Left-aligned
Second table column -- Center-aligned
Third table column -- Right-aligned

Then you should set the value of
the align attribute to LCR.

Following is the example showing usage of <table> element.


<wml>



<card title="WML Tables">
<p>
<table columns="3" align="LCR">
<tr>
<td>Col 1</td>
<td>Col 2</td>
<td>Col 3</td>
</tr>

<tr>
<td>A</td>
<td>B</td>
<td>C</td>
</tr>

<tr>
<td>D</td>
<td>E</td>
<td>F</td>
</tr>
</table>
</p>
</card>

</wml>


WML - Links

WML provides you an option to link various cards using links and then navigate through
different cards.

There are two WML elements, <anchor> and <a>, which can be used to create WML
links.

WML <anchor> Element:



The <anchor>...</anchor> tag pair is used to create an anchor link. It is used together
with other WML elements called <go/>, <refresh> or <prev/>. These elements are called
task elements and tell WAP browsers what to do when a user selects the anchor link

You can enclose Text or image along with a task tag inside <anchor>...</anchor> tag
pair.

The <anchor> element supports the following attributes:

title cdata Defines a text identifying the link

Following is the example showing usage of <anchor> element.


<wml>

<card title="Anchor Element">
<p>
<anchor>
<go href="nextpage.wml"/>
</anchor>
</p>
<p>
<anchor>
<prev/>
</anchor>
</p>
</card>

</wml>




WML <a> Element:

The <a>...</a> tag pair can also be used to create an anchor link and always a preferred
way of creating links.

You can enclose Text or image inside <a>...</a> tags.

The <a> element supports the following attributes:

href URL Defines URL of the liked page
title cdata Defines a text identifying the link

Following is the example showing usage of <a> element.


<wml>

<card title="A Element">
<p> Link to Next Page:
<a href="nextpage.wml">Next Page</a>
</p>
</card>

</wml>




WML - Tasks

A WML task is an element that specifies an action to be performed by the browser,
rather than something to be displayed. For example, the action of changing to a new
card is represented by a <go> task element, and the action of returning to the previous
card visited is represented by a <prev> task element. Task elements encapsulate all the
information required to perform the action.

WML provides following four elements to handle four WML tasks called go task, pre task,
referesh task and noop taks.

The <go> Task:

As the name suggests, the <go> task represents the action of going to a new card.

The <go> element supports the following attributes:

href URL Gives the URL of the new card. Relative URLs are
resolved relative to the current card
method get Specifies the method that should be used to
post fetch the deck. This must be one of the values
get or post, corresponding to the GET and POST
methods of HTTP.

When using method="get", the data is sent as
an request with ? data appended to the url. The
method has a disadvantage, that it can be used
only for a limited amount of data, and if you
send sensitive information it will be displayed on
the screen and saved in the web server's logs. So
do not use this method if you are sending
password etc.

With method="post", the data is sent as an
request with the data sent in the body of the
request. This method has no limit, and sensitive



information is not visible in the URL
sendreferer true If set to true, the browser sends the URL of the
false current deck along with the request. This URL is
sent as a relative URL if possible. The purpose of
this is to allow servers to perform simple access
control on decks, based on which decks are
linking to them. For example, using HTTP, this
attribute is sent in the HTTP Referer header.
accept- charset_list Specifies a comma- or space-separated list of
charset character sets that can encode data sent to the
server in a POST request. The default value is
"unknown".

Following is the example showing usage of <go> element.


<wml>

<card title="GO Element">
<p>
<anchor>
Chapter 2 : <go href="chapter2.wml"/>
</anchor>
</p>
</card>
</wml>

Another example showing how to upload data using Get Method


<wml>

<p>
<anchor>
Using Get Method
<go href="chapter2.wml?x=17&y=42" method="get"/>



</anchor>
</p>
</card>
</wml>

Another example showing how to upload data using <setvar> element.


<wml>

<p>
<anchor>
Using setvar:
<go href="chapter2.wml">
<setvar name="x" value="17"/>
<setvar name="y" value="42"/>
</go>
</anchor>
</p>
</card>
</wml>

Another example showing how to upload data using <postfiled> element


<wml>

<p>
<anchor>
Using setvar:
<go href="chapter2.wml" method="get">
<postfield name="x" value="17"/>
<postfield name="y" value="42"/>
</go>
</anchor>
</p>
</card>
</wml>



The <prev> Task:

The <prev> task represents the action of returning to the previously visited card on the
history stack. When this action is performed, the top entry is removed from the history
stack, and that card is displayed again, after any <setvar> variable assignments in the
<prev> task have taken effect.

If no previous URL exists, specifying <prev> has no effect.

The <prev> element supports the following attributes:


Following is the example showing usage of <prev> element.


<wml>

<card title="Prev Element">
<p>
<anchor>
Previous Page :<prev/>
</anchor>
</p>
</card>
</wml>

One situation where it can be useful to include variables in a <prev> task is a login page,
which prompts for a username and password. In some situations, you may want to clear
out the password field when returning to the login card, forcing the user to reenter it.
This can be done with a construct such as:


<wml>

<card title="Prev Element">
<p>
<anchor>



<prev>
<setvar name="password" value=""/>
</prev>
</anchor>
</p>
</card>
</wml>

The <refresh> Task:

The <refresh> task is the simplest task that actually does something. Its effect is simply
to perform the variable assignments specified by its <setvar> elements, then redisplay
the current card with the new values. The <go> and <prev> tasks perform the same
action just before displaying the new card.

The <refresh> task is most often used to perform some sort of "reset" action on the card.

The <refresh> element supports the following attributes:


Following is the example showing usage of <refresh> element.


<wml>

<card title="Referesh Element">
<p>
<anchor>
Refresh this page:
<go href="test.wml"/>
<refresh>
<setvar name="x" value="100"/>
</refresh>
</anchor>
</p>
</card>
</wml>

The <noop> Task:



The purpose of the <noop> task is to do nothing (no operation).

The only real use for this task is in connection with templates

The <noop> element supports the following attributes:


Following is the example showing usage of <noop> element.


<wml>

<card title="Noop Element">
<p>
<do type="prev" label="Back">
<noop/>
</do>
</p>
</card>
</wml>

WML - Inputs

WML provides various options to let a user enter information through WAP application.

First of all, we are going to look at the different options for allowing the user to make
straight choices between items. These are usually in the form of menus and submenus,
allowing users to drill down to the exact data that they want.

WML <select> Element:

The <select>...</select> WML elements are used to define a selection list and the
<option>...</option> tags are used to define an item in a selection list. Items are
presented as radio buttons in some WAP browsers. The <option>...</option> tag pair
should be enclosed within the <select>...</select> tags.

This element support the following attributes:




iname text Names the variable that is set with the index
result of the selection
ivalue text Sets the pre-selected option element
multiple true Sets whether multiple items can be selected.
false Default is "false"

name text Names the variable that is set with the result of
the selection
tabindex number Sets the tabbing position for the select element
title text Sets a title for the list
value text Sets the default value of the variable in the
"name" attribute

Following is the example showing usage of these two elements.


<wml>

<card title="Selectable List">
<p> Select a Tutorial :
<select>
<option value="htm">HTML Tutorial</option>
<option value="xml">XML Tutorial</option>
<option value="wap">WAP Tutorial</option>
</select>
</p>
</card>

</wml>

When you will load this program it will show you following screen:



Once you highlight and enter on the options it will display following screen:

You wan to privide option to select multiple options then set multiple attribute to true as
follows:


<wml>

<p> Select a Tutorial :
<select multiple="true">
<option value="htm">HTML Tutorial</option>
<option value="xml">XML Tutorial</option>
<option value="wap">WAP Tutorial</option>
</select>
</p>
</card>

</wml>

This will give you a screen to select multiple options as follows:



WML <input> Element:

The <input/> element is used to create input fields and input fields are used to obtain
alphanumeric data from users.


name text The name of the variable that is set with the
result of the user's input
maxlength number Sets the maximum number of characters the
user can enter in the field
emptyok true Sets whether the user can leave the input
false field blank or not. Default is "false"

format A Sets the data format for the input field.
a Default is "*M".
N
X A = uppercase alphabetic or punctuation
x characters
M a = lowercase alphabetic or punctuation
m characters
*f N = numeric characters
nf X = uppercase characters
x = lowercase characters
M = all characters
m = all characters
*f = Any number of characters. Replace
the f with one of the letters above to specify
what characters the user can enter
nf = Replace the n with a number from 1 to 9
to specify the number of characters the user
can enter. Replace the f with one of the
letters above to specify what characters the
user can enter
size number Sets the width of the input field
tabindex number Sets the tabbing position for the select
element
type text Indicates the type of the input field. The
password default value is "text". Password field is used
to take password for authentication purpose.
value text Sets the default value of the variable in the



"name" attribute

Following is the example showing usage of this element.


<wml>

<card title="Input Fields">
<p> Enter Following Information:<br/>
Name: <input name="name" size="12"/>
Age : <input name="age" size="12" format="*N"/>
Sex : <input name="sex" size="12"/>
</p>
</card>

</wml>

This will provide you following screen to enter required information:

WML <fieldset> Element:

The <fieldset/> element is used to group various input fields or selectable lists.








<wml>

<card title="Grouped Fields">
<p>
<fieldset title="Personal Info">
Sex : <input name="sex" size="12"/>
</fieldset>
</p>
</card>

</wml>

This will provide you following screen to enter required information. This result may
differ browser to browser.

WML <optgroup> Element

The <optgroup/> element is used to group various options together inside a selectable
list.








<wml>

<p>
<select>
<optgroup title="India">
<option value="delhi">Delhi</option>
<option value="mumbai">Mumbai</option>
<option value="hyderabad">Hyderabad</option>
</optgroup>
<optgroup title="USA">
<option value="ohio">Ohio</option>
<option value="maryland">Maryland</option>
<option value="washington">Washingtone</option>
</optgroup>
</select>
</p>
</card>

</wml>

When a user loads above code then it will give two options to be selected:

When a user select any of the options then only it will give final options to be selected.
So if user selects India then it will show you following options to be selected:



WML - Submit Data to Server

Many times you will want your users to submit some data to your server. Similar
to HTML FormWML also provide a mechanism to submit user data to web server.

To submit data to the server in WML, you need the <go>...</go> along with <postfield/>
tags. The <postfield/> tag should be enclosed in the <go>...</go> tag pair.

To submit data to a server, we collect all the set WML variables and use <postfield>
elements to send them to the server. The <go>...</go> elements are used to set posting
method to either POST or GET and to specify a server side script to handle uploaded
data.

In previous chapters we have explained various ways of taking inputs form the users.
These input elements sets WML variables to the entered values. We also know how to
take values from WML variables. So now following example shows how to submit three
fields name, age and sex to the server.



<wml>

<card id="card1" title="WML Form">
<p>
Sex : <select name="sex">
<option value="male">Male</option>
<option value="female">Female</option>
</select>
<anchor>
<go method="get" href="process.php">
<postfield name="name" value="$(name)"/>
<postfield name="age" value="$(age)"/>
<postfield name="sex" value="$(sex)"/>
</go>
Submit Data



</anchor>
</p>
</card>

</wml>

When you download above code on your WAP device, it will provide you option to enter
three fields name, age and sex and one link Submit Data. You will enter three fields and
then finally you will select Submit Data link to send entered data to the server.

The method attribute of the <go> tag specifies which HTTP method should be used to
send the form data.

If the HTTP POST method is used, the form data to be sent will be placed in the message
body of the request. If the HTTP GET method is used, the form data to be sent will be
appended to the URL. Since a URL can only contain a limited number of characters, the
GET method has the disadvantage that there is a size limit for the data to be sent. If the
user data contains non-ASCII characters, you should make use of the POST method to
avoid encoding problems.

There is one major difference between HTML and WML. In HTML, the name attribute of
the <input> and <select> tags is used to specify the name of the parameter to be sent,
while in WML the name attribute of the <postfield> tag is used to do the same thing. In
WML, the name attribute of <input> and <select> is used to specify the name of the
variable for storing the form data.

Next chapter will teach you how to handle uploaded data at server end.

WML - Server Side Scripts

If you already know how to write server side scripts for Web Application then for you this
is very simple to write Server Side program for WML applications. You can use your
favorite server-side technology to do the processing required by your mobile Internet
application.

At the server side, the parameter name will be used to retrieve the form data.

Consider the following example from previous chapter to submit name, age and sex of a
person:



<wml>

<card id="card1" title="WML Form">



<p>
Sex : <select name="sex">
<option value="male">Male</option>
<option value="female">Female</option>
</select>
<anchor>
<go method="get" href="process.php">
<postfield name="name" value="$(name)"/>
<postfield name="age" value="$(age)"/>
<postfield name="sex" value="$(sex)"/>
</go>
Submit Data
</anchor>
</p>
</card>

</wml>

WML and PHP

Now we can write a server side script to handle this submitted data in using either PHP,
PERL, ASP or JSP. I will show you a server side script written in PHP with HTTP GET
method.

Put the following PHP code in process.php file in same directory where you have your
WML file.

<?php echo 'Content-type: text/vnd.wap.wml'; ?>
<?php echo '<?xml version="1.0"?'.'>'; ?>

<wml>

<card id="card1" title="WML Response">
<p>
Data received at the server:<br/>
Name: <?php echo $_GET["name"]; ?><br/>
Age: <?php echo $_GET["age"]; ?><br/>
Sex: <?php echo $_GET["sex"]; ?><br/>
</p>
</card>

</wml>



If you are using HTTP POST method then you have to write PHP script accordingly to
handle received data. While sending output back to the browser, remember to set the
MIME type of the document to "text/vnd.wap.wml".

WML - Events

Event in ordinary language can be defined as something happens. In
programming event is identical in meaning, but with one major difference. When
something happens in a computer system, the system itself has to (1) detect that
something has happened and (2) know what to do about it.

WML language also supports events and you can specify an action to be taken whenever
an event occurs. This action could be in terms of WMLScript or simply in terms of WML.

WML supports following four event types:

onenterbackward: This event occurs when the user hits a card by normal
backward navigational means. That is, user presses the Back key on a later card
and arrives back at this card in the history stack.
onenterforward: This event occurs when the user hits a card by normal forward
navigational means.
onpick: This is more like an attribute but it is being used like an event. This event
occurs when an item of a selection list is selected or deselected.
ontimer: This event is used to trigger an event after a given time period.

These event names are case sensitive and they must be lowercase.

WML <onevent> Element:

The <onevent>...</onevent> tags are used to create event handlers. Its usage takes the
following form:

<onevent type="event_type">
A task to be performed.
</onevent>

You can use either go, prev or refresh task inside <onevent>...</onevent> tags against an
event.

The <onevent> element supports the following attributes:

type onenterbackward Defines a type of event occured.
onenterforward
onpick
ontimer




Following is the example showing usage of <onevent> element. In this example whenever
you try to go back from second card to first card then onenterbackward occurs which
moves you to card number three. Copy and past this program and try to play with it.


<wml>
<onevent type="onenterbackward">
<go href="#card3"/>
</onevent>

<card id="card1" title="Card 1">
<p>
<anchor>
<go href="#card2"/>
Go to card 2
</anchor>
</p>
</card>
<p>
<anchor>
<prev/>
Going backwards
</anchor>
</p>
</card>
<p>
Hello World!
</p>
</card>
</wml>

WML - Timer

Previous chapter has described how events are triggered by the users and how do we
handle them using event handlers.

Sometime, You may want something to happen without the user explicitly having to
activate a control. Yes, WML provides you ontimer event to handle this.



The ontimer event is triggered when a card's timer counts down from one to zero, which
means that it doesn't occur if the timer is initialized to a timeout of zero.

You can bind a task to this event with the <onevent> element. Here is the syntax:

<onevent type="ontimer">
A task to be performed.
</onevent>

Here a task could be <go>, <prev> or <refresh>.

WML <timer> Element:

A timer is declared inside a WML card with the <timer> element. It must follow the
<onevent> elements if they are present. (If there are no <onevent> elements, the <timer>
must be the first element inside the <card>.) No more than one <timer> may be present
in a card.

The <timer> element supports the following attributes:

name text Sets a name for the element.
value number Specifies the timer after which timer will be expired.
Timeouts are specified in units of a tenth of a second.
class class_data Sets a class name for the element.
id element A unique ID for the element.
ID

Following is the example showing usage of <timer> element.


<wml>

<card id="splash" title="splash">
<onevent type="ontimer">
<go href="#welcome"/>
</onevent>
<timer value="50"/>
<p>
<a href="#welcome">Enter</a>
</p>
</card>



<card id="welcome" title="Welcome">
<p>
Welcome to the main screen.
</p>
</card>
</wml>

When you load this program it shows you following screen:

If you do not select given Enter option then after 5 seconds you will be directed
to Welcome page and following screen will be displayed automatically.

WML - Template

The <template> is used to apply <do> and <onevent> elements to all cards in a deck.
This element defines a template for all the cards in a deck and the code in the
<template> tag is added to each card in the deck.

You can override a <do> element of a template by defining another <do> element with
the samename attribute value in a WML card.

The <template> element supports the following attributes:

onenterbackward URL Occurs when the user navigates into a card
using a "prev" task
onenterforward URL Occurs when the user navigates into a card
using a "go" task



ontimer URL Occurs when the "timer" expires
class class Sets a class name for the element.
data
id element A unique ID for the element.
ID

Following is the example showing usage of <go> element.


<wml>
<template>
<do name="main_menu" type="accept" label="Chapters">
<go href="chapters"/>
</do>
<do name="menu_1" type="accept" label="Chapter 1">
<go href="#chapter1"/>
</do>
</do>
</do>
</do>
</template>

<card id="chapters" title="WML Tutorial">
<p>
Select One Chapter:<br/>
<anchor>
Chapter 1: WML Overview
</anchor><br />

<anchor>
Chapter 2: WML Environment
</anchor><br />

<anchor>
Chapter 3: WML Syntax



</anchor><br />

<anchor>
Chapter 4: WML Elements
</anchor><br />
</p>
</card>

<card id="chapter1" title="WML Tutorial Ch1">
<p>
<em>Chapter 1: WML Introduction</em><br/>
...
</p>
</card>

<p>
<em>Chapter 2: WML Environment</em><br/>
...
</p>
</card>

<p>
<em>Chapter 3: WML Syntax</em><br/>
...
</p>
</card>

<p>
<em>Chapter 4: WML Elements</em><br/>
...
</p>
</card>
</wml>

This will produce following menu and now you can navigate through all the chapters:


WML-Tutorial

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