By default, instances of movie
clip symbols in a Flash document’s library cannot be dynamically
created (that is, created using only ActionScript). This is because each
symbol that is exported for use in ActionScript adds to the size
of your SWF file, and it’s recognized that some symbols might not
be intended for use on the stage. For this reason, in order to make
a symbol available in ActionScript, you must specify that the symbol
should be exported for ActionScript.
To export a symbol for ActionScript:
Select the symbol
in the Library panel and open its Symbol Properties dialog box.
If necessary, activate the Advanced settings.
In the Linkage section, activate the Export for ActionScript
This will activate the Class and Base Class fields.
default, the Class field is populated with the symbol name, with
spaces removed (for example, a symbol named “Tree House” would become “TreeHouse”).
To specify that the symbol should use a custom class for its behavior,
enter the full name of the class including its package in this field.
If you want to be able to create instances of the symbol in ActionScript,
but don’t need to add any additional behavior, you can leave the
class name as-is.
The Base Class field’s value defaults to flash.display.MovieClip.
If you want your symbol to extend the functionality of another customer
class, you can specify that class’s name instead, as long as that
class extends the Sprite (or MovieClip) class.
Press the OK button to save the changes.
At this point,
if Flash can’t find a linked SWC file or an external ActionScript
file with a definition for the specified class (for instance, if
you didn’t need to add additional behavior for the symbol), a warning
A definition for this class could not be found in the classpath, so one will be automatically generated in the SWF file upon export.
can disregard this warning if your library symbol does not require
unique functionality beyond the functionality of the MovieClip class.
you do not provide a class for your symbol, Flash will create a
class for your symbol equivalent to this one:
public class ExampleMovieClip extends MovieClip
public function ExampleMovieClip()
If you do want to add extra ActionScript functionality
to your symbol, add the appropriate properties and methods to the
code structure below. For example, suppose you have a movie clip
symbol containing a circle of 50 pixels width and 50 pixels height,
and the symbol is specified to be exported for ActionScript with a
class named Circle. The following code, when placed in a Circle.as
file, extends the MovieClip class and provides the symbol with the
additional methods getArea() and getCircumference():
public class Circle extends MovieClip
public function Circle()
public function getArea():Number
// The formula is Pi times the radius squared.
return Math.PI * Math.pow((width / 2), 2);
public function getCircumference():Number
// The formula is Pi times the diameter.
return Math.PI * width;
The following code, placed on a keyframe on Frame
1 of the Flash document, will create an instance of the symbol and
display it on the screen:
var c:Circle = new Circle();
This code demonstrates
ActionScript-based instantiation as an alternative to dragging individual
assets onto the Stage. It creates a circle that has all of the properties
of a movie clip and also has the custom methods defined in the Circle class.
This is a very basic example—your library symbol can specify any
number of properties and methods in its class.
instantiation is powerful, because it allows you to dynamically
create large quantities of instances that would be tedious to arrange manually.
It is also flexible, because you can customize each instance’s properties as
it is created. You can get a sense of both of these benefits by
using a loop to dynamically create several Circle instances. With
the Circle symbol and class described previously in your Flash document’s
library, place the following code on a keyframe on Frame 1:
var totalCircles:uint = 10;
for (i = 0; i < totalCircles; i++)
// Create a new Circle instance.
var c:Circle = new Circle();
// Place the new Circle at an x coordinate that will space the circles
// evenly across the Stage.
c.x = (stage.stageWidth / totalCircles) * i;
// Place the Circle instance at the vertical center of the Stage.
c.y = stage.stageHeight / 2;
// Change the Circle instance to a random color
c.transform.colorTransform = getRandomColor();
// Add the Circle instance to the current timeline.
// Generate random values for the red, green, and blue color channels.
var red:Number = (Math.random() * 512) - 255;
var green:Number = (Math.random() * 512) - 255;
var blue:Number = (Math.random() * 512) - 255;
// Create and return a ColorTransform object with the random colors.
return new ColorTransform(1, 1, 1, 1, red, green, blue, 0);
This demonstrates how you can create and customize
multiple instances of a symbol quickly using code. Each instance
is positioned based on the current count within the loop, and each
instance is given a random color by setting its transform property
(which Circle inherits by extending the MovieClip class).