Clearing a Saved
Form in WML
As
you may notice, after you have inputted some data in a form, the form
data is saved. The data you inputted in the form remains there no
matter you refresh or navigate backwards/forwards to the WML card.
As
mentioned earlier, each input field or selection list created is
associated with a variable. The data entered in the input field or
the value of the option chosen in a selection list is stored in the
variable. For example, if you include the line <input
name="myName"/> in a card, the characters entered into
the input field will be stored in the variable myName.
WML
variables have a global scope. Once a value is assigned to a
variable, it will remain there even if you navigate to another card.
When an earlier form is displayed again, the WAP browser will take
the values saved in the variables and use them as the initial values
of the input fields or selection lists. For example, if you include
the line <input name="myName"/> in a card,
the value assigned to the myName
variable earlier will be used to initialize the input field.
Hence,
to clear a saved form, you have to write some markup code to clear
the variables associated with the input fields and selection lists of
the form.
The
following WML examples demonstrate several ways to clear a saved
form. Below is the markup code of the first example. What we want to
do is to ensure our form is in the default state every time it is
displayed.
(clearSavedFormEg1.wml)
<?xml
version="1.0"?>
<!DOCTYPE wml PUBLIC
"-//WAPFORUM//DTD WML 1.3//EN"
"http://www.wapforum.org/DTD/wml13.dtd">
<wml>
<card
id="card1" title="Clear Saved Forms">
<onevent
type="onenterforward">
<refresh>
<setvar
name="myName" value=""/>
<setvar
name="myGender" value=""/>
<setvar
name="favorite_tutorial_part"
value=""/>
</refresh>
</onevent>
<onevent
type="onenterbackward">
<refresh>
<setvar
name="myName" value=""/>
<setvar
name="myGender" value=""/>
<setvar
name="favorite_tutorial_part"
value=""/>
</refresh>
</onevent>
<p>
Hello,
welcome to our WML tutorial.<br/>
What's
your name?<br/>
<input
name="myName"/><br/>
Are you a boy or
a girl?<br/>
<select
name="myGender">
<option value="Boy">I
am a boy</option>
<option value="Girl">I
am a girl</option>
</select><br/>
Which
part of our WML tutorial do you like?<br/>
<select
name="favorite_tutorial_part"
multiple="true">
<option value="Part
1">Part 1</option>
<option value="Part
2">Part 2</option>
<option value="Part
3">Part 3</option>
<option value="Part
4">Part
4</option>
</select><br/><br/>
<anchor>
<go
method="get"
href="clearSavedFormEg1Proc.asp">
<postfield
name="name" value="$(myName)"/>
<postfield
name="gender" value="$(myGender)"/>
<postfield
name="tutorial_part"
value="$(favorite_tutorial_part)"/>
</go>
Submit
Data
</anchor>
</p>
</card>
</wml>
Here
is the ASP file that handles the form data submitted to the server.
It simply prints out the name-value pairs received.
(clearSavedFormEg1Proc.asp)
<?xml
version="1.0"?>
<!DOCTYPE wml PUBLIC
"-//WAPFORUM//DTD WML 1.3//EN"
"http://www.wapforum.org/DTD/wml13.dtd">
<%
Response.ContentType = "text/vnd.wap.wml" %>
<wml>
<card
id="card1" title="Submission
Result">
<p>
Data
received at the server:<br/>
Name: <%
=Request.QueryString("name") %><br/>
Gender:
<% =Request.QueryString("gender") %><br/>
Which
part of our WML tutorial do you like?
<%
=Request.QueryString("tutorial_part")
%><br/>
</p>
</card>
</wml>
In
the above WML example, the WAP browser clears the variables myName,
myGender and
favorite_tutorial_part when the onenterforward
event or the onenterbackward event occurs. We make use of both
the onenterforward and
onenterbackward events
so that no matter if a user reaches the card in the forward or
backward direction, the form variables will be reset to an empty
string.
The
drawback of the above method is that if the user does not go back to
the original card, the saved form is not cleared. In some situations
such as when the form data is confidential, it is better to clear the
saved form as soon as possible. In our second WML example, we clear
the saved form in the submission result card. The markup is shown
below:
(clearSavedFormEg2.wml)
<?xml
version="1.0"?>
<!DOCTYPE wml PUBLIC
"-//WAPFORUM//DTD WML 1.3//EN"
"http://www.wapforum.org/DTD/wml13.dtd">
<wml>
<card
id="card1" title="Clear Saved
Forms">
<p>
Hello,
welcome to our WML tutorial.<br/>
What's
your name?<br/>
<input
name="myName"/><br/>
Are you a boy or
a girl?<br/>
<select
name="myGender">
<option value="Boy">I
am a boy</option>
<option value="Girl">I
am a girl</option>
</select><br/>
Which
part of our WML tutorial do you like?<br/>
<select
name="favorite_tutorial_part"
multiple="true">
<option value="Part
1">Part 1</option>
<option value="Part
2">Part 2</option>
<option value="Part
3">Part 3</option>
<option value="Part
4">Part
4</option>
</select><br/><br/>
<anchor>
<go
method="get"
href="clearSavedFormEg2Proc.asp">
<postfield
name="name" value="$(myName)"/>
<postfield
name="gender" value="$(myGender)"/>
<postfield
name="tutorial_part"
value="$(favorite_tutorial_part)"/>
</go>
Submit
Data
</anchor>
</p>
</card>
</wml>
(clearSavedFormEg2Proc.asp)
<?xml
version="1.0"?>
<!DOCTYPE wml PUBLIC
"-//WAPFORUM//DTD WML 1.3//EN"
"http://www.wapforum.org/DTD/wml13.dtd">
<%
Response.ContentType = "text/vnd.wap.wml" %>
<wml>
<card
id="card1" title="Submission Result">
<onevent
type="onenterforward">
<refresh>
<setvar
name="myName" value=""/>
<setvar
name="myGender" value=""/>
<setvar
name="favorite_tutorial_part"
value=""/>
</refresh>
</onevent>
<p>
Data
received at the server:<br/>
Name: <%
=Request.QueryString("name") %><br/>
Gender:
<% =Request.QueryString("gender") %><br/>
Which
part of our WML tutorial do you like?
<%
=Request.QueryString("tutorial_part")
%><br/>
</p>
</card>
</wml>
In
the above WML example, the onenterforward event is triggered
when the card in the ASP file is loaded. The event action is to clear
the variables myName,
myGender and
favorite_tutorial_part.
An
alternative is to use the newcontext attribute of the <card>
tag. If the newcontext attribute value is set to true, the WAP
browser will be reset to the initial state. All WML variables (and
the navigational history) will be cleared as a result.
(clearSavedFormEg3Proc.asp)
<?xml
version="1.0"?>
<!DOCTYPE wml PUBLIC
"-//WAPFORUM//DTD WML 1.3//EN"
"http://www.wapforum.org/DTD/wml13.dtd">
<%
Response.ContentType = "text/vnd.wap.wml" %>
<wml>
<card
id="card1" title="Submission Result"
newcontext="true">
<p>
Data
received at the server:<br/>
Name: <%
=Request.QueryString("name") %><br/>
Gender:
<% =Request.QueryString("gender") %><br/>
Which
part of our WML tutorial do you like?
<%
=Request.QueryString("tutorial_part")
%><br/>
</p>
</card>
</wml>
The
drawback of clearing a saved form in the submission result card is
that we do not know which card a user will browse next. If a user
types some data in the form but does not select the submit anchor
link (for example, he/she may press the Back button of the mobile
phone or may enter the URL of another WAP site), the submission
result card will not be reached and so the saved form will remain in
the memory.
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