Actionscript 3 EventListener - actionscript-3

Question

I am fairly new to actionscript 3 and I would like to know how can I make EventListener to work only once. Right now it works after every click, but I need to get it work only with first click.
After click it displays a ball on the stage where the click was made. I need to get to the point where only one ball appears and after that click should do nothing.
my code:
stage.addEventListener(MouseEvent.CLICK, onClick,false,0,true);
function onClick(evt:MouseEvent):void {
var ball:MovieClip = new Ball();
ball.x = stage.mouseX;
ball.y = stage.mouseY;
addChildAt(ball,0);
}

Answer 1

You need to call removeEventListener() as follows:
stage.addEventListener(MouseEvent.CLICK, onClick,false,0,true);
function onClick(evt:MouseEvent):void {
stage.removeEventListener(MouseEvent.CLICK, onClick);
var ball:MovieClip = new Ball();
ball.x = stage.mouseX;
ball.y = stage.mouseY;
addChildAt(ball,0);
}

Answer 2

One possible solution is to remove the EventListener.
stage.addEventListener(MouseEvent.CLICK, onClick,false,0,true);
function onClick(evt:MouseEvent):void {
stage.removeEventListener(MouseEvent.CLICK, onClick);
var ball:MovieClip = new Ball();
ball.x = stage.mouseX;
ball.y = stage.mouseY;
addChildAt(ball,0);
}
Another solution is a simple bool variable, in case you need the eventlistener for something else.
var clickedOnce:Boolean = false;
stage.addEventListener(MouseEvent.CLICK, onClick,false,0,true);
function onClick(evt:MouseEvent):void {
if(!clickedOnce){
clickedOnce = true;
var ball:MovieClip = new Ball();
ball.x = stage.mouseX;
ball.y = stage.mouseY;
addChildAt(ball,0);
}
}