How to hitTestObject MC items of an array with a MC target? - actionscript-3

Question

I have items in an array, each is a movieclip, which play at delayed intervals of 1 second and a target movieclip (carTarget) controlled by arrow keys where the aim is to avoid a collision with the array items (obstacleArray[i]). I have been attempting to create a hitTestObject statement to notify when there is a collision. However I have received errors such as parameter hitTestObject most be non-null and cannot figure out how to resolve it.
//obstacles
function randomSort(a:*, b:*):Number
{
if (Math.random() < 0.5) return -1;
else return 1;
}
var obstacleArray:Array = [obstacleCar,obstacleCar2,obstacleCar3];
obstacleArray.sort(randomSort);
trace(obstacleArray);
trace(obstacleArray.length);
//OBSTACLE START DELAY
var timerPlay:Timer = new Timer(1000,1);
timerPlay.addEventListener(TimerEvent.TIMER, ontimerPlay);
timerPlay.start();
var i:int = 0;
var timerDelay:Timer = new Timer(1000, 3);
function ontimerPlay(evt:TimerEvent):void{
obstacleArray[i].addEventListener(Event.ENTER_FRAME,checkHitTest);
//FOR EACH OBSTACLE
timerDelay.addEventListener(TimerEvent.TIMER, ontimerDelay);
timerDelay.start();
}
function checkHitTest(event:Event):void{
if(carTarget.hitTestObject(obstacleArray[i]))
{
trace("HIT!");
}
}
function ontimerDelay(evt:TimerEvent):void{
obstacleArray[i].play();
trace(obstacleArray[i]);
i++;
}

Answer 1

Most likely, the problem is in this block of code:
function checkHitTest(event:Event):void{
if(carTarget.hitTestObject(obstacleArray[i]))
{
trace("HIT!");
}
}
After i changes with the timer calls, then obstacleArray[i] will be null or worse - another object other than the one you need to check.
You should change this to:
function checkHitTest(event:Event):void{
if(carTarget.hitTestObject(event.target))
{
trace("HIT!");
}
}
event.target will get the current obstacle calling the checkHitTest from Enterframe event

Answer 2

It is very likely that hitTestObject does not exist at the moment you're trying to use it. From the code you shared, I do not see where you create it in your code. So, assuming carTarget is an object on the stage and that it has the property or object hitTestObject initialized when you want to use it -assuming those things, then you need to make sure that when this code is running, that object still exists.