Flash MX 2004 Games : Art to ActionScript

Flash MX 2004 Games
11
12
}
13 //Method to return property values
14 function dump():String {
15 return("Hi, my job is " + job +
16 " and my feet are " + feet + " inches long.");
17
18 }
}
Listing 7.6
A class definition always starts with the keyword ‘class’, followed by the name you have chosen
for the class. All remaining code is between curly brackets. Any variables the class contains are usually
declared next along with their data type. A class usually will have what is called a ‘constructor’
function. A function is simply a block of code that is given a name; following the name will be
ordinary brackets. Contained inside the brackets will be none or several parameters separated by
commas. The code for the function is contained between curly brackets. A function can return
a value; if so, it is a good idea to specify the type of value that is to be returned. If you don’t
actually create a constructor function for your class then Flash will create one for you. In this
simple example we have the class ‘Performer’ that contains two variables, ‘feet’ and ‘job’. It has
one method ‘dump’, which returns a string description of the current instance of the class. It also
has a constructor function; these must have the same name as the class. So having created the code
that defines the class, how do we use it?
Using a user-defined class
1 var Clown:Performer = new Performer("Clown", 14);
2 var RingMaster:Performer = new Performer("Ringmaster", 10);
3 var Helper:Performer = new Performer();
4
5 trace(Clown.dump());
6 trace(RingMaster.dump());
7 trace(Helper.dump());
Listing 7.7
First it is vital that the syntax for the class definition is correct, second the class definition file must
be in the same folder as the ‘fla’ and must have the same name as the class being defined with an
‘as’ extension. As long as these simple rules are kept to, the use of a class is simplicity itself. You
use the ‘var’ keyword followed by the variable name and a colon. After the colon place your class
name. Then use the equals sign, the keyword ‘new’ and then the name of the class, open brackets
and then set the parameters. In this example we first give the ‘job’ name and then the feet size.
Notice that at line 3 of Listing 7.7 we pass no parameters. This is OK and Flash will set the values
to undefined. Lines 9 and 10 of Listing 7.6 set the values to a default value if undefined. In lines
94