ActionScript 3.0 Design Patterns

Video Player Concrete State Application | 367

Because the application at this stage only provides traces, you will need to use the

Flash Test (Control➝Test or Control➝Test Project) to see the output. Open a new

Flash document, and, in the Document class window, type inTestState. The follow-

ing should appear in the Output window:

Video Player is On

--Play State--

--Stop State--

Begin playing

A new state is set

You're already playing

Stop playing.

A new state is set

You're already stopped

Both theVideoWorksclass and thePlayStateandStopStateclasses include atrace

statement to indicate their instantiation, and appear as soon as you test the script.

Because the initial state is Stop, it changes states to the Play state when the first

startPlay( )method is invoked. Also, because you’re changing states, atracestate-

ment from theVideoWorksclass indicates a state change. However, when the second

startPlay( )method is invoked a second time, the same method in a different con-

text recognizes that it’s already in the Play state and simply indicates that you’re

already playing. When you press the Stop button, you move to the Stop state, set-

ting a new state, but on the second press, the same function in this new context rec-

ognizes that you’re already in the Stop state, and indicates that fact.

Video Player Concrete State Application

All that you’ve seen so far has been the output astrace( )statements to help under-

stand how a State design pattern and State machine works. To add something use-

ful, we need to include a reference to both aNetStreamobject and a string for

referencing an FLV file. However, we need a string reference only for playing the

video, because we can stop it simply by closing theNetStreaminstance. The follow-

ing four scripts set up the state machine to actually play and stop a video. All of the

trace statements have been left in place.

With the implementation of an application that actually plays a video, we’ll need to

import the necessary parts. Because theNetStreamclass is used in the interface and

the two states, each of those files will need to import the class. However, while the

VideoWorksclass uses both thePlayandStopclasses, it does not have to import the

NetStream( ) class. This is because it’s already imported in thePlay andStop classes.

The following five listings, Example 10-7 through Example 10-11, should be entered

into an ActionScript file and saved with the captions as the filenames. Save all the

files in the same folder.