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

Both instances employ the templateMethod( ) function, but as you will see when you
test the application, the results are very different. Open a new Flash document file,
and in the Document class window, type in BuildShed. When you test the application,
you’ll see the following in the Output window:
SteelShed
Designing Steel Shed
Ok I'll need some corregated sheet metal.
Better get some steel fasteners too.
Now I can put all my tools away.
WoodShed
Designing Wood Shed
I'll do it with 1 X 12's for the walls.
The rest I'll do with 2 X 4's.
Now I can put all my tools away.
In this output, you can see the Template Method at work. In the first instance, you
can see that it shows the SteelShed concrete class has been invoked. All the output is
uniquely relevant to the steel shed except for the last line before the wood shed output.
That last line is the locked up operation from the abstract class, ShedMaker.
Then, the WoodShed instance gets an entirely different set of results when it invokes
the templateMethod( ), with the exception of the last line.
From this example, we hope you can better see the conceptual structure of the
Template Method. All the calls are made from the higher-level ShedMaker class to the
lower-level concrete class instances through the templateMethod( ) function. So even
though the lower level override functions define the specifics of some of the
operations within the template method, the actual call follows the Hollywood Principle
and calls downward through the template method.
Selecting and Playing Sound and Video
Considering how Flash handles sound and video, they both share some actions in
common. For example, both need to have filenames to play, and both have to somehow
have a “play” command. Using the Template Method, we should be able to key
in on those two functions of getting a filename and playing, and placing them into an
algorithm. However, because of the differences between the two media, we’ll leave
the details up to the concrete classes. The locked operation that’ll be in the main
abstract class will be a text header.
Setting Up the Format
The initial abstract class containing an algorithm for a filename selector and playcommand
operation is pretty simple, because the operations have no content. A
third operation that adds a text message to the top of the screen will be locked, and
while it’s relatively simple, it requires importing a number of packages. Open a new
344 | Chapter 9: Template Method Pattern