ActionScript 3.0 Design Patterns

When to Use the Singleton Pattern | 121

To test this particular implementation, you will need a slightly more elaborate Flash

document file. The following steps show what you need to do.

1. Open a new Flash document and save it in the same folder as yourTuner.as file.


2. Using the Oval tool, draw an oval with a radius of 15 on the stage. Select the
   oval, and then press the F8 button to open the Convert to Symbol dialog box.
   Type inSongPlayin the Name window, and select Button for the Type. Click the
   Export for ActionScript checkbox in the Linkage group. The class name should
   showSongPlayand the base class will showflash.display.SimpleButton. Click
   OK. Delete the button from the stage. (It still remains in the Library.)


3. Open the Properties panel, and, in the Document class window, type in
   DoMusicBtn. Save the file once more.


4. In the folder where you’ve saved the ActionScript (.as) and Flash document files
   (.fla), add two MP3 files using the file names shown in Example 3-14. (You can
   change the names in your MP3 files or the names in Example 3-14.)


5. Test the application by pressing Ctrl + Enter (Command + Return on the Mac).

You should see three buttons appear. The two buttons on the left let you select one

of the two MP3 files, and the one on the right will stop whatever is currently play-

ing. If you click either of the buttons on the left while a tune is still playing, it’ll stop

the tune and start play from the beginning of the selected tune.

Using Multiple References in a Shopping Cart

This final example of a Singleton design pattern shows how a Singleton instance can

have multiple references and still maintain accuracy. Like the previous examples, this

one’s also simple, with the focus on both the role of the Singleton design and some

insights into the Singleton structure

The online Shopping Cart is really nothing more than a conceptual image of a digital

accumulator. As each new item is added to the cart, the most current entry is accu-

mulated, and at the time of checkout, this total is computed with applicable ta xand

playTune.playMe ("blues.mp3");
}
function doTwo (e:MouseEvent):void
{
playTune.playMe ("class1.mp3");
}
function doStop (e:MouseEvent):void
{
playTune.stopMe ( );
}
}
}

Example 3-14. DoMusicBtn.as