Acces of undefined property cerc - actionscript-3

Question

I have this code in AS3:
package clase
{
import flash.display.MovieClip;
import flash.events.Event;
/**
* ...
* #author cry
*/
public class CercNegru extends MovieClip
{
var growthRate:Number = 2;
cerc.addEventListener(Event.ENTER_FRAME,grow);
public function CercNegru()
{
}
private function grow(e:Event):void
{
trace("asdda");
}
}
}
When you run this program receive error:
Line 12 1120: Access of undefined property cerc.
Line 12 1120: Access of undefined property grow.
I put an image to understand better :
Can you help me to solve this problem please?
Thanks in advance!

Answer 1

The errors are because in class files, all functional code needs to live inside a function.
So take this line, which is just floating in the class:
cerc.addEventListener(Event.ENTER_FRAME,grow);
And move into the constructor (assuming you want it to run right away when you instantiate the class):
public function CercNegru()
{
cerc.addEventListener(Event.ENTER_FRAME,grow);
}
In class files, the constructor (which is the function whose name exactly matches the class name), is what get's called you use the new keyword.
So doing new CercNegru() will call that function.
NOW, I'm also assuming that this class file is attached to FlashPro library object, and you have something on the timeline with an instance name of cerc. (if that is not the case, then that is the reason for your error)
Timeline stuff though, isn't always available in the constructor, so you may need to wait until the instance has been added to the screen.
public var cerc:MovieClip; //you may want to create a reference to the timeline item, so you get compile time checking
public function CercNegru()
{
this.addEventListener(Event.ADDED_TO_STAGE, addedToStage);
}
private function addedToStage(e:Event):void {
this.removeEventListener(Event.ADDED_TO_STAGE, addedToStage);
//this is the equivalent of timeline code now
cerc.addEventListener(Event.ENTER_FRAME,grow);
}

Answer 2

package clase
{
import flash.display.MovieClip;
import flash.events.Event;
/**
* ...
* #author cry
*/
public class CercNegru extends MovieClip
{
var growthRate:Number = 2;
var cerc:DisplayObject; // ADD THIS
public function CercNegru()
{
cerc.addEventListener(Event.ENTER_FRAME,grow);
}
private function grow(e:Event):void
{
trace("asdda");
}
}
}
As the error says cerc is undefined. So you should define it. Assuming that your 'cerc' is a Sprite,
var cerc:Sprite;