ActionScript 3.0 Design Patterns.pdf - VideoTutorials-bg.com

To create a class, we need a public constructor function within a package. Because
we cannot create a private class within a package, we’ll have to create one outside a
package, and then somehow get it to work inside a package. So, using a single .as
file, the following script first creates a public class, closes the package, and then creates
a private class outside the package. The private class is then called from within
the public class. Example 3-2 shows how this is done.
Example 3-2. PublicClass.as
1 package
2 {
3 import flash.display.Sprite;
4 public class PublicClass extends Sprite
5 {
6 public function PublicClass( )
7 {
8 PrivateClass.alert( );
9 }
10 }
11 }
12 //End of Package
13 //**************
14 //Private class
15 class PrivateClass
16 {
17 public function PrivateClass( )
18 {
19
20 public static function alert( ):void
21 {
22 trace("This is from a private class");
23 }
24 }
Save the file as PublicClass.as, and, in an FLA file, type in PublicClass as the Document
class, and save the FLA file as TestPrivate.fla. When you test the program, you
will see:
This is from a private class
in the Output panel. Notice in Line 8 that the class, PrivateClass, is employed simply
by typing the class name and the method. No constructor statement is used at all.
Creating a Private Class Instance
Keeping in mind the implementation in Example 3-1, we have to work out a way for
the class constructor to act like a private class. If the private class can be part of the
instantiation method (getInstance( )), then we’ll be able to have the same effect as a
private class constructor.
104 | Chapter 3: Singleton Pattern