WML and WMLScript

WMLBrowser

This chapter talks about the WMLBrowser. WMLBrowser is a library that deals exclusively with the Browser environment. This chapter deals with the various functions that deal with the Browser environment. It also explains how to create a variable; how to obtain the value of a variable; how WMLScript and WML work with each other; and how the program control passes from WML to WMLScript and back.

Earlier, we had discussed two functions - one called getVar and the other called setVar. The function getVar returns the value of the variable. But if the variable doesn't exist, it doesn't give you an error, it simply returns null. If the value of the variable is invalid, i.e. if the variable name is incorrect or if it contains a space, then the function will return an invalid value, otherwise it will return a string. Remember that even though the variable value is a number, it will return a string. We have already informed you that there is a seamless conversion between numbers and strings. The function getvar returns a null string if the variable doesn't exist.

Screen 8. 1

aaa.wmls

extern function abc()

{

var aa;

aa=WMLBrowser.setVar("aaa","Hi");

if ( aa)

Dialogs.alert("true");

else

Dialogs.alert("false");

}

If you input a wrong variable name, for instance- a space, it will return an invalid value; otherwise, it returns a string. Even if the variable contains a number, or a boolean (true or false) value, it will still return a string. This conversion from number to string, and from boolean to string takes effect automatically.

The function setVar will always return a true, if it is able to accomplish what you ask it to do. In our example, setVar has been asked to create a variable called aaa.

· If the variable already exists, it is given the specified value, in this case it is "hi".

· But, if the variable doesn't exist, it is freshly created.

This is all that the setVar function does. Actually, it should have aptly been called as createVar because, if the variable doesn't exist, it creates it. In this case, our variable aa doesn't exist. So, the function Dialogs.alert gets called.

We learnt about go href in the WML section. With go you could navigate from one card to another. A similar function is available in the WMLBrowser library. The next program demonstrates it.

Screen 8. 2

aaa.wmls

extern function abc()

{

WMLBrowser.go("a33.wml");

}

a33.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>

<p>

Hi $aa

</p>

</card>

</wml>

Screen 8. 3

Just as you have go and prev in WML, you have ...prev here, which takes you to the previous page, but first Dialogs.alert gets called. This implies that it occurs right at the end. So, you can have as many gos and prevs as you like, but they only take effect after they go to WML.

aaa.wmls

extern function abc()

{

WMLBrowser.prev();

Dialogs.alert("hi");

}

Screen 8. 4

Screen 8. 5

When WMLScript completes execution, it goes back to WML. It is at this stage that WML gets triggered to execute a go or a prev. That is why they say that the go and the prev override each other. And if the last one is an empty one, you are effectively disabling it.

The card in WML had an attribute called newcontext. In WMLScript, it is in the form of a function.

a11.wml

<?xml version="1.0"?>

<!DOCTYPE wml PUBLIC "-//WAPFORUM//DTD WML 1.1//EN" "http://www.wapforum.org/DTD/wml_1.1.xml">

<wml>

</go>

</do>

<p>

Hello $aa

</p>

</card>

</wml>

aaa.wmls

extern function abc()

{

var bb;

bb = WMLBrowser.getVar("aa");

Dialogs.alert(bb);

WMLBrowser.newContext();

bb = WMLBrowser.getVar("aa");

Dialogs.alert(bb);

}

Screen 8. 6

Screen 8. 7

First we create a variable called aa in WML. Then we assign it a value of hi using setvar. The wmls file displays Hi first and then a blank screen. WMLBrowser.newcontext clears everything, including the variables and the navigational links.

Screen 8. 8

aaa.wmls

extern function abc()

{

var aa;

aa = WMLBrowser.getCurrentCard();

Dialogs.alert(aa);

}

The function getCurrentCard returns a11.wmlc. It is the compile file that calls the script.