| Just like a regular class, a MovieClip subclass can itself be extended by another subclass. When a parent class is defined outside of its corresponding movie clip symbol (as in the very first Ball example in this chapter), its child subclass can be defined by: Remember also to invoke the parent's constructor function from the child constructor. For example, the following code shows how to create a subclass, Baseball, of our existing class, Ball: // Baseball class constructor org.moock.Baseball = function ( ) { // ... init code ... // Invoke Ball class constructor super( ); } // Set Baseball's superclass to Ball org.moock.Baseball.prototype = new org.moock.Ball( ); // Associate the Baseball class with its own Library symbol Object.registerClass("baseballSymbol", org.moock.Baseball); However, when both the subclass (Ball) and the sub-subclass (Baseball) are defined inside a movie clip symbol's #initclip block, we must ensure that the subclass is initialized before any of the sub-subclasses. To do so, we use the order parameter of the #initclip pragma, which is a nonnegative integer specifying the execution order of a particular #initclip block, relative to all other #initclip blocks in the movie. Those #initclip blocks with lower order numbers are always executed before those with higher ones. All #initclip blocks without a specified order are executed before those with a specified order. For example, to create a Baseball class inside the movie clip baseballSymbol, we must change the first line of our Ball class code to: #initclip 0 Then we can create our Baseball class as follows: // Use a higher #initclip order than Ball uses, guaranteeing that Ball // will be available before this code runs. #initclip 1 // = = = = = = = = = = = = = = = = = = = = = = = = = = // Create namespace in which to store classes // = = = = = = = = = = = = = = = = = = = = = = = = = = if (_global.org = = undefined) { _global.org = new Object( ); } if (_global.org.moock = = undefined) { _global.org.moock = new Object( ); } // = = = = = = = = = = = = = = = = = = = = = = = = = = // Create the Baseball class // = = = = = = = = = = = = = = = = = = = = = = = = = = /* * Baseball Class. Extends Ball. * Version: 1.0.0 * Desc: A movie clip subclass for depicting baseballs * * Constructor Params: * signature -The ball's signature * * Methods: * setSignature( ) -Set the signature on the ball */ /* * Class Constructor. Parameters are passed by attachMovie( )'s initObj. */ org.moock.Baseball = function ( ) { // Create Instance properties. this.sig = null; // Initialize instance before calling Ball constructor. (Otherwise, // Ball will delete the params object before we get a chance to use it.) this.setSignature(this.params.signature); // Invoke Ball class constructor. super( ); // No need to delete params object, because the Ball constructor does that. }; /* * Set Ball as Baseball's superclass. */ org.moock.Baseball.prototype = new org.moock.Ball( ); /* * Associate the Library's baseballSymbol with the Baseball class */ Object.registerClass("baseballSymbol", org.moock.Baseball); /* * Instance Methods */ /* * Method: Ball.setSignature( ) * Desc: Sets the ball's signature * * Params: * newSig -The ball's new signature */ org.moock.Ball.prototype.setSignature = function (newSig) { this.sig = newSig; }; #endinitclip Note that multiple #initclip blocks can share a single order position. For example, if we create three subclasses of Ball, we can set all of their #initclip order parameters to 1. All that matters is that the Ball's #initclip order is lower than all its subclasses. | 
