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

Example 10-2. VideoWorks.as (continued)
18 state.startPlay( );
19 }
20 public function stopPlay( ):void
21 {
22 state.stopPlay( );
23 }
24 public function setState(state:State):void
25 {
26 trace("A new state is set");
27 this.state=state;
28 }
29 public function getState( ):State
30 {
31 return state;
32 }
33 public function getPlayState( ):State
34 {
35 return this.playState;
36 }
37 public function getStopState( ):State
38 {
39 return this.stopState;
40 }
41 }
42 }
43
Initially, in lines 6-8, the script instantiates three State objects—one of each of the
two we designed (PlayState and StopState), and one (state) that acts as a variable to
hold the current state. Because the state machine begins in the Stop state, the state
variable is assigned the Stop state. (This works just like the light switch before you
change it from the off state to the on state.)
Next, the two behaviors from the State interface are specified in terms of the current
state’s context (lines 16-23). We’re going to have to add some code to the two state
classes for it to work with the context class, but for now, think of what will happen
in the two different states when those behaviors are executed. For example, in the
Play state, the startPlay( ) method doesn’t do anything, but in the Stop state, it
switches to the Play state.
Finally, add the getter and setter methods (lines 24-40). We need a total of sixmethods—a
set and get function for each of the three state instances. The setters return
nothing and the getters return a State object.
Completing and testing the abstract state machine
To get everything working, we need to revise the state classes to include the reference
to the context—VideoWorks. Save Example 10-3 as StopState.as.
364 | Chapter 10: State Pattern