Assigning a class to a movie clip symbol

Using ActionScript 2.0, you can create a class that extends the behavior of the built-in MovieClip class and then assign that class to a movie clip library symbol using the Linkage Properties dialog box. Whenever you create an instance of the movie clip to which the class is assigned, it assumes the properties and behaviors defined by the class assigned to it. (For more information about ActionScript 2.0, see Creating Custom Classes with ActionScript 2.0.)

In a subclass of the MovieClip class, you can provide method definitions for the built-in MovieClip methods and event handlers, such as onEnterFrame and onRelease. In the following procedure, you'll create a class called MoveRight that extends the MovieClip class; MoveRight defines an onPress handler that moves the clip 20 pixels to the right whenever the user clicks the movie clip. In the second procedure, you'll create a movie clip symbol in a new Flash (FLA) document and assign the MoveRight class to that symbol.

To create a movie clip subclass:

1. Create a new directory called BallTest.
2. Create a new ActionScript file by doing one of the following:
   • (Flash MX Professional 2004) Select File > New, and select ActionScript file from the list of document types.
   • (Flash MX 2004) Create a text file in your preferred text editor.
3. Enter the following code in your script:

   // MoveRight class -- moves clip to the right 20 pixels when clicked
   class MoveRight extends MovieClip {
   	function onPress() {
   		this._x += 20;
   	}
   }
   

4. Save the document as MoveRight.as in the BallTest directory.

To assign the class to a movie clip symbol:

1. In Flash, select File > New, select Flash Document from the list of file types, and click OK.
2. Using the Oval tool, draw a circle on the Stage.
3. Select the circle, and select Modify > Convert to Symbol.
4. In the Convert to Symbol dialog box, select Movie Clip as the symbol's behavior, and enter ball_mc in the Name text box.
5. Select Advanced to show the options for Linkage, if they aren't already showing.
6. Select the Export for ActionScript option, and type MoveRight in the AS 2.0 Class text box. Click OK.
7. Save the file as ball.fla in the BallTest directory (the same directory that contains the MoveRight.as file).
8. Test the movie (Control > Test Movie).

   Each time you click the ball movie clip, it moves 20 pixels to the right.

If you create component properties for a class and want a movie clip to inherit those component properties, you need to take an additional step: with the movie clip symbol selected in the Library panel, select Component Definition from the Library options menu and enter the new class name in the AS 2.0 Class box. For more information, see "Creating Components" in Using Components.

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