how understand url not reachable (IOError) ? - actionscript-3

Question

There are images inside of folder names like Slide1.jpg,Slide2.jpg, until Slide20.jpg. But program doesn't know how many images inside of folder. I dont want to count them also.(lets say total number of images = 100). But when press nextBtn until Slide20.jpg program will take:
Error #2044: Unhandled IOErrorEvent:. text=Error #2036: Load Never
Completed
When program Catches that error logically, it means there is no file name like Slide21.jpg. Which means total image number is 20. I want to go back when take at first time that error. Thanks for any advice
var totalImages=100;
var imageNumber=1;
var myLoader:Loader = new Loader();
//************LOADING IMAGES TO STAGE********************//
//elearningau.com/nondynamic/
var myRequest:URLRequest = new URLRequest("http://elearning.com/upandshow/Images/Slide"+imageNumber+".JPG");
myLoader.load(myRequest);
addChildAt(myLoader,1)
rightButton.addEventListener(MouseEvent.CLICK, nextImage);
function nextImage(event:MouseEvent){
if(imageNumber<totalImages)
{
imageNumber++;
} else {
imageNumber = 1;
}
reload();
}
function reload(){
removeChild(myLoader);
myRequest= new URLRequest("http://elearning.com/upandshow/Images/Slide"+imageNumber+".JPG");
myLoader.load(myRequest);
addChildAt(myLoader, 1);
}

Answer 1

You need to listen for errors:
myLoader.addEventListener(IOErrorEvent.IO_ERROR, ioErrorHandler);
function ioErrorHandler(event:IOErrorEvent):void {
// this means there was an error - do whatever you want
}