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 use the Linkage Properties dialog box to assign that class to a movie clip library symbol. 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 Example: Writing custom classes.)

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:

Create a new directory called BallTest.
Select File > New, and select ActionScript file from the list of document types to create a new ActionScript file.

Enter the following code in your script file:

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

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

To assign the class to a movie clip symbol:

In Flash, select File > New, select Flash Document from the list of file types, and click OK.
Using the Oval tool, draw a circle on the Stage.
Select the circle, and select Modify > Convert to Symbol.
In the Convert to Symbol dialog box, select Movie Clip as the symbol's behavior, and enter ball_mc in the Name text box.
Select Advanced to show the options for Linkage, if they aren't already showing.
Select the Export for ActionScript option, and type MoveRight in the Class text box. Click OK.
Save the file as ball.fla in the BallTest directory (the same directory that contains the MoveRight.as file).
Test the Flash document (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 pop-up menu and enter the new class name in the Class box.