Webmaster''''s Guide to the Wireless Internet part 18 ppt

Table 4.2Keywords in WMLScript Examining WMLScript Data Types WMLScript supports five built-in data types: ■ Integer ■ Floating Point ■ String ■ Boolean ■ Invalid To declare a variable,

Comments are either encapsulated within a pair of “/*” and “*/” or are pre-ceded with the “//” combination, like this:

/* This is a block of

comments that spans multiple lines

*/

// This is a single line of comment

// This is another line of comment

WMLScript 1.1 also reserves a set of keywords that have special meaning to the compiler.They are shown in Table 4.2

Table 4.2Keywords in WMLScript

Examining WMLScript Data Types

WMLScript supports five built-in data types:

■ Integer

■ Floating Point

■ String

■ Boolean

■ Invalid

To declare a variable, use the var keyword.There is no need to explicitly

declare the data types;WMLScript will handle them internally.The following illustrates how WMLScript automatically converts the variable to the appropriate data type:

var month=12;

var price=5.95;

var msg="Hello World!";

var printName=true;

var except=Invalid;

The Invalid type is used to differentiate itself from the other data types, for

example:

if (5/0=Invalid) { // codes here }

Examining WMLScript Operators

Similar to most programming languages,WMLScript supports the sets of opera-tors shown in Tables 4.3, 4.4, 4.5, 4.6, and 4.7

Table 4.3Assignment Operators

Operator Description

x = x + y

x = x – y

x = x * y

x = x / y

x div= y is equivalent to x = x div y

dividend) and then assign; for example, x %= y is equivalent to

x = x % y

<<= Bitwise left shift and then assign; for example, x <<= y is

equivalent to x = x << y

>>= Bitwise right shift with sign and then assign; for example,

x >>= y is equivalent to x = x >> y

Continued

>>>= Bitwise right shift zero file and then assign; for example,

x >>>= y is equivalent to x = x >>> y

&= Bitwise AND and then assign; for example, x &= y is equivalent

to x = x & y

to x = x ^ y

to x = x | y

Table 4.4Binary Arithmetic Operators

Operator Description

dividend

<< Bitwise left shift

>> Bitwise right shift and sign

>>> Bitwise shift right with zero fill

& Bitwise AND

Table 4.5Unary Arithmetic Operators

Operator Description

Table 4.3Continued

Operator Description

Continued

++ Pre/post increment

Table 4.6Logical Operators

Operator Description

&& Logical AND

Table 4.7Comparison Operators

Operator Description

<= Less than or equal

>= Greater than or equal

Inequality WMLScript also supports the conditional operators For example, the fol-lowing if-else statement:

if (x==0) {

x = 1;

} else { x=10;

}

can be rewritten as:

x = 0 ? 1 : 10

Table 4.5Continued

Operator Description

Examining WMLScript Control Structures

WMLScript supports the if construct for making decisions and the while and for

loops for repetitive execution

Using the If Statement

The if statements allows decisions to be made based on the result of a condition.

For example, the following code snippet will calculate the average if the total is more than zero; otherwise it will assign the average to be zero:

if (total>0) {

average = sum / total;

} else {

average = 0;

}

Using the While Loop

The while loop executes a block of instruction repeatedly as long as the condition

is true For example, the following sums up all the integers from 1 to 5:

var num = 5;

var sum = 0;

while (num>=1) {

sum += num—;

}

Using the For Loop

The for loop executes a block of instruction repeatedly for a finite number of

times For example:

var result = 1;

for (var i=1; i<=num; i++) // loop counter i starts at 1, ends when result *= i; // i is less than or equal to num i is

// incremented by 1 in each loop

Using the Break Keyword

The break keyword interrupts the loop within a while or for loop For example:

while (num>1) { sum += num—; // add up num and decrement num by 1

if (sum>20) // if the sum is more than 20, break; // break out of the loop }

Using the Continue Keyword

The continue keyword allows execution of either a for or while loop to continue,

thereby skipping the rest of the block For example:

var num = 20;

for (var i=1; i<=num; i++) {

if (i%2==0) // if no remainder (meaning it is an even number), continue; // continue the loop

Console.print(i) // else print out the odd number }

Using WMLScript Libraries

The WMLScript specification contains the following libraries:

■ Lang Library Contains functions that relate to the language core

■ Float Library Contains functions that perform floating point operations

■ String Library Contains functions that perform string operations

■ URL Library Contains a set of functions for handling absolute URLs and relative URLs

■ WMLBrowser Library Contains functions by which WMLScript can access the associated WML context

■ Dialogs Library Contains a set of typical user-interface functions

Libraries are named collections of functions that belong logically together.To call these functions, simply specify the library name followed by a dot (.) sepa-rator and the function name with the appropriate parameters.We will take a look

at some of the examples in the following sections

The library collection can be extended by emulator vendors for debugging purposes For example, the UP.Simulator contains the Console library to help developers in debugging

Functions in the Class Libraries

Within the libraries there are functions.Table 4.8 shows the functions within the various libraries described in the previous section.We will be making use of some

of these functions in the examples that follow

Learning to Interpret WMLScript

Let’s look at our first example on how WML interacts with WMLScript In this example, we will look at how a WML deck (see Figure 4.3) calls a WMLScript

program (Figure 4.4) using the <go> element.The WMLScript program in this

example contains one function defined with the extern keyword It also illustrates

the use of functions located in the libraries

Figure 4.3 Example1.wml—WML Deck Calling a WMLScript Program

<?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="card1" title="Card 1">

<p>

Say hello to WMLScript!

<do type="accept" label="Hello">

<go href="Example1.wmls#Hello" />

</do>

</p>

</card>

</wml>

Figure 4.4Example1.wmls—WMLScript Program Displaying an Alert

extern function Hello() {

Dialogs.alert("A big Hi from WMLScript!");

}

Table 4.8

toString trim

Dissecting the Code

The WML deck (shown in Figure 4.3) contains a <go> element, which points to

a WMLScript file:

<go href="Example1.wmls#Hello" />

To link a WML deck to the WMLScript file, specify the filename of the

WMLScript file in the href attribute of the <go> element.The name following

the # symbol is the function name in the WMLScript.

Within the WMLScript file (see Figure 4.4), we have a function named

Hello() defined with the extern keyword:

extern function Hello() {

}

Only functions in WMLScript with the extern keyword preceding the

func-tion name may be called by a WML deck In this case, the funcfunc-tion named

Hello()accepts no input parameters

Dialogs.alert("A big Hi from WMLScript!");

This line simply tries to display an alert on the user’s screen In this case, we

use the alert() function from the Dialogs library Using the Nokia WAP Toolkit,

you should see the screens shown in Figure 4.5

NOTE

WMLScript statements end with a semicolon (;) Readers familiar with JavaScript should feel right at home!

Figure 4.5Linking a WML Deck to a WMLScript File

Performing Mathematical Operations Using WMLScript

The next example that we will illustrate is performing mathematical operations, using WMLScript to calculate the factorial of a number.This example uses a WML deck to prompt the user to enter a number (see Figure 4.6).The number

is then passed to the WMLScript program for calculation (see Figure 4.7).This example illustrates looping construct in WMLScript as well as setting variable values in WMLScript and how it is passed back to the WML deck

Figure 4.6Example2.wml—WML Deck to Prompt the User to Enter a Number

<?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="card1" title="Card 1">

<p>

Factorial machine: <br/>

Enter a number:

<input type="text" name="num" />

<do type="accept" label="Calculate!">

<go href="Example2.wmls#Calculate($(num))" />

</do>

</p>

</card>

<card id="card2" title="Card 2">

<p>

$num ! is $(result)

</p>

</card>

</wml>