344 | Chapter 9: Template Method Pattern
Both instances employ thetemplateMethod( )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 inBuildShed. When you test the applica-
tion, 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 theSteelShedconcrete class has been invoked. All the output is
uniquely relevant to the steel shed except for the last line before the wood shed out-
put. That last line is the locked up operation from the abstract class,ShedMaker.
Then, theWoodShedinstance gets an entirely different set of results when it invokes
thetemplateMethod( ), 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-levelShedMakerclass to the
lower-level concrete class instances through thetemplateMethod( )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 Princi-
ple 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 some-
how 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 play-
command 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