Minimalist Example of an MVC Pattern | 435The view needs to hold references to both the model and controller as it initiates
communication with them as shown in Figure 12-1. Both the model and controller
instances are passed to the view in its constructor. Also, the view in our example
needs a reference to the stage to register itself to receive key press events.
In addition to drawing the user interface, theViewclass does a couple of important
tasks. It registers with the model to receive update events, and delegates to the con-
troller to handle user input. In our example, the view does not have an external
visual representation on the stage, but displays the model state in the output panel. It
needs to receive key press events, and registers the method calledonKeyPress( )to
receiveKEY_DOWNevents from the stage (line 20). The second task is to register a lis-
tener method calledupdate( )to receive aCHANGEevent from the model (line 16). On
notification of a change, theupdate( )method reads the character code for the last
key pressed from the model and prints it to the output panel using the trace function.
Building the MVC Triad
We have looked at the individual implementations of the three elements that make
up the MVC pattern. However, there has to be a client that initializes each element
and builds the MVC model. There’s no real building involved – all that needs to be
11 public function View(aModel:IModel, oController:
IKeyboardInputHandler,target:Stage)
12 {
13 this.model = aModel;
14 this.controller = oController;
15
16 // register to receive notifications from the model
17 model.addEventListener(Event.CHANGE, this.update);
18
19 // register to receive key press notifications from the stage
20 target.addEventListener(KeyboardEvent.KEY_DOWN,
21
22 }
23
24 private function update(event:Event):void
25 {
26 // get data from model and update view
27 trace(model.getKey( ));
28 }
29
30 private function onKeyPress(event:KeyboardEvent):void
31 {
32 // delegate to the controller (strategy) to handle it
33 controller.keyPressHandler(event);
34 }
35 }
36 }Example 12-5. View.as (continued)