addChild( ) , creating a new movie clip in Action Script 2.0 / Action Script 3.0

Creating new instances of a class has been greatly simplified in ActionScript 3.0. In previous versions of ActionScript, you needed to call createEmptyMovieClip() or createTextField() if you wanted to create a new MovieClip or TextField. Now, in ActionScript 3.0, you can simply call new MovieClip() or new TextField() directly, as shown in the following examples:

// AS2
this.createEmptyMovieClip("mc", this.getNextHighestDepth());
mc.beginFill(0xFF0000);
mc.moveTo(0, 0);
mc.lineTo(100, 0);
mc.lineTo(100, 80);
mc.lineTo(0, 80);
mc.lineTo(0, 0);
mc.endFill();
mc._x = 80;
mc._y = 60;

The previous code creates a new movie clip instance, draws a red rectangle which is 100×80 pixels, and moves the instance to 80,60 on the Stage. Compare that to the following code which does the exact same thing, although using the new drawRect() method instead of having to use the moveTo() and lineTo() methods:

// AS3
var mc:MovieClip = new MovieClip();
mc.graphics.beginFill(0xFF0000);
mc.graphics.drawRect(0, 0, 100, 80);
mc.graphics.endFill();
mc.x = 80;
mc.y = 60;
addChild(mc);

Note that there are a few differences. Most obvious is the use of the MovieClip() constructor instead of ActionScript 2.0′s createEmptyMovieClip(). Other notable differences are that the drawing methods (beginFill(), drawRect(), and endFill()) are called on the graphics property instead of on the instance itself. Also, in ActionScript 3.0, the x and y properties aren’t prefixed with underscores. Finally, in ActionScript3.0 the instance isn’t added to the display list until you explicitly call the addChild() method.

TIP: In addition to the drawRect() method, you can also call the drawCircle(), drawEllipse(), ordrawRoundRect() methods to draw shapes.

If you wanted to instead draw a rounded rectangle, instead of calling the lineTo() and curveTo() methods, you could use the new drawRoundRect() method, as shown in the following code:

mc.graphics.drawRoundRect(0, 0, 100, 80, 15, 15);