Actionscript - Introduktion - Interaction Design Umeå

Report
Introduction to
Flash ActionScript 3.0
Variables & Data types
Thomas Lövgren, Flash developer
[email protected]
Variables
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A variable is a place to store information
It has a name and a type
Variables are used to make the code dynamic
Values can generally be accessed or changed at any time
An identifier (usually a letter, word, or phrase) that is linked to a
value stored in the system's memory or an expression that can be
evaluated
Depending on the type system of a programming language,
variables may only be able to store a specified data type
Naming variables
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Variable names can only contain letters, numbers, and dollar
signs ($)
All variables must have unique names
Start variables with a lowercase letter
Variables are case-sensitive
Use mixed case for concatenated words
Don't use reserved words: this, menu, private, video, etc.
Don't use the same variable name with different cases
Keep variables as short as possible while retaining clarity
Example, with strict datatyping:
var xSpeed:Number;
Data types
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The Data type defines the type of data a variable or ActionScript
element can hold
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Primitive data types (Top level data types):
 Boolean, int, Null, Number, String, uint, and void
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Complex data types:
 Object, Array, Date, Error, Function, RegExp, XML,
and XMLList
Variable syntax
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Example of the different parts and structure of a variable
declaration/population
Data type: String (1/2)
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Strings are sequences of characters, numbers and punctuation
marks. These are enclosed within double (") quotation marks
The String data type represents a sequence of 16-bit characters
The default value for a variable declared with the String data type is
null
//declaration
var myURL_string:String;
//assignment
myURL_string = "www.flashkit.com";
//declaration and assignment
var myURL_string:String = "www.flashkit.com";
Datatype: String (2/2)
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Example of some methods for the String object are:
Substring, charAt, replace, toUpperCase, split, join etc
//declare variable
var my_string:String;
//assignment and concatenation
my_string = ”Hi ”+”there!”; //traces to Hi there!
//getting substring
var sub_string:String = my_string.substring(3, my_string.length);
//making all characters uppercase
var upper_string:String = sub_string.toUpperCase();
trace(upper_string); //yields THERE!
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Tip! Declare your variables first (on top)
Data type: Number (1/2)
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The Number data type can represent integers, unsigned integers,
and floating-point numbers
The Number data type uses the 64-bit double-precision format
The default value is NaN
//declaration
var length:Number;
//assignment
length = 1100;
length = -22;
length = 0.00002234;
length = 100/3; //traces to 33.3333333333333
length = 1/0; //traces to Infinity
Data type: Number (2/2)
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Variable declaration, assignment and initialization
//declaration
var height:Number;
//assignment
height = 200;//literal value
height = anotherVariable;//value from another variable
//initialization(declaration and assignment on the same code line)
var width:Number = 300;
//check max and min values
Number.MAX_VALUE == 1.79769313486231e+308
Number.MIN_VALUE == 4.940656458412467e-324
Data type: int
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New data type in AS3
The int data type is a 32-bit integer between -2,147,483,648 and
2,147,483,647
Integers only work in whole numbers and ignore the decimal
value, always rounding down
The default value for variables that are of data type uint is 0
//example 1
var myInt:int = -15;
var myInt2:int = 3500;
//example 2
var num:int = 2.5;
var product:int = num + 2;
trace(product); //4, the decimal will be ignored
Data type: unit
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New data type in AS3
The uint (Unsigned Integer) data type is a 32-bit unsigned
integer between 0 and 4,294,967,295
Unsigned integer or any non-negative whole number
The default value for variables that are of data type uint is 0
var myUnit:unit = 1;
var mySecondUnit:unit = 3500;
var unsignedInteger:uint; //0
Number, int or unit?
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To maximize performance, it’s recommended that we use the
Number data type only for integer values larger than the int and uint
types can store or for floating-point numbers.
To store a floating-point number, include a decimal point in the
number
If we omit a decimal point, the number will be stored as an integer
Data type: Boolean
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Boolean represents a boolean value, possible values: true or false
Converts the parameter expression to a Boolean value and returns
true or false
Default vaule is false
//declaration of a boolean variable
var isLoaded:Boolean;
//assignmet
isLoaded = true;
Default Values (1/2)
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A Default value is the value that a variable contains before you set
its value
You initialize a variable when you set its value for the first time
If you declare a variable, but do not set its value, that variable is
uninitialized
The value of an uninitialized variable depends on its data type
Default Values (2/2)
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The following table describes the default values of variables,
organized by data type
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Note! For variables of type Number, the default value is NaN (not a number)
Array (1/2)
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Arrays are lists of data under which each item is identified by its
order within the list
The first element in an Array has index 0
An array can be made up of primitive type values like strings,
numeric values, booleans or complex type values like other arrays
or objects
var music_array:Array = new Array();
music_array = ["Metallica", "Bruce Springsteen", "U2", "Iron
Maiden", "David Gray", "Van Morrison"];
music_array.length //traces the length of the array
music_array[1]; //traces Bruce Springsteen
var my_array:Array = [5,"Hello!",{a:5, b:7}]; //complex array
Array (2/2)
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Example of some methods for the Array object are:
slice, join, concat, push, pop, reverse etc.
var music_array:Array = new Array();
music_array = ["Metallica", "Bruce Springsteen", "U2", "Iron
Maiden", "David Gray", "Van Morrison"];
//slice(startIndex, endIndex)
music_array.slice(2,4); //traces U2, Iron Maiden
Typecasting
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Sometimes we need to typecast a data type into another (for some
reson), for exampe if we load XML data (numbers) and Flash
interpret it like string vaules
Here’s an example of how we can typecast a string into a number
var my_string:String = "50";
var my_num:Number = 20;
var answer:Number;
trace(my_string + my_num); //traces 5020
//typecast the string to a number data type
trace(Number(my_string) + my_num); //traces 70
Scope
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Scope is the realm or space in wich an object (variable) lives
In ActionScript 3.0, variables are always assigned the scope of the
function or class in which they are declared
Entrance into that scope typically begins a variable's lifetime and
exit from that scope typically ends its lifetime
function localScope(){
var strLocal:String = "local";
}
localScope();
trace(strLocal); //error because strLocal is not defined globally
Arithmetic operators
Arithmetic operators
+, -, *, /, %
++, - +=, -=, *=, /=, %=
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Increment ++, and decrement - Increments/decrements a variable by 1
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var x:Number = 10;
x++;
trace(x); //traces 11
x--;
trace(x); //traces 10
Precedence
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The answer depends on operator precedence
var i:Number;
i = 12 + 3 * 10 / 2; //traces 27
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You can override precedence by using parenteses
var i:Number;
i=(12 + 3) * 10 / 2;
trace(i); //traces 75

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