as3 array of objects - movement with constant speed - arrays

Question

Ok, so I have some experience with as3 and some of the basics. But this problem has been stumping me for so long. I tried to do a workaround based on what I currently know about as3. But somehow either i get an error message or it just doesn't do anything at all. Here is the code that i'm trying to solve.
var zombieCount:Array = new Array();
var helltime:Timer = new Timer(1500);
helltime.addEventListener(TimerEvent.TIMER, spawnzombies)
helltime.start();
function spawnzombies(happened:TimerEvent){
var zombie1:Zombie = new Zombie();
zombieCount.push(zombie1);
stage.addChild(zombieCount[zombieCount.length - 1]);
zombie1.x = 135 + (330*Math.random())
zombie1.y = -29
stage.addEventListener(Event.ENTER_FRAME, move_zombie)
function move_zombie(happened:Event){
for(var i:int; i < zombieCount.length; i++){
zombieCount[i].y = zombieCount[i].y + 1;
if(zombieCount[i].hitTestObject(border)){
stage.removeChild(zombieCount[i]);
zombieCount.shift();
trace(zombieCount.length);
}
}
}
}

Answer 1

While this may not be inclusive of everything wrong, here are at least a few of the issues I see.
Inline function issue:
Inside your timer tick handler (spawnZombies), you create an inline function called move_zombie and then add an enter frame handler that calls that function.
The issue here, is that every tick of the timer, will then create a whole new copy of that function, and add ANOTHER enter frame handler. This will create huge problems after a few timer ticks.
Break that move_zombie function OUT OF the spawn function:
eg:
helltime.addEventListener(TimerEvent.TIMER, spawnzombies)
helltime.start();
stage.addEventListener(Event.ENTER_FRAME, move_zombie);
function move_zombie(......
function spawnzombies(.....
Iteration issue:
In your for loop:
for(var i:int; i < zombieCount.length; i++){
zombieCount[i].y = zombieCount[i].y + 1;
if(zombieCount[i].hitTestObject(border)){
stage.removeChild(zombieCount[i]);
zombieCount.shift();
trace(zombieCount.length);
}
}
You are not initializing your i value. While this will default it to 0, it's still a good idea for readability to initialize it.
So your iterating forward from 0 to the end of the array. However, if your hit test succeeds, you then use the shift method of the array. This removes the first item of the array (irrespective of what value i is at the time). This will remove the wrong item, plus mess up what zombieCount[i] refers to (because the amount of items has now changed after doing shift, so the next iteration zombieCount[i] will be a reference to same item as the previous iteration).
Instead of what you're currently doing, use the splice method to remove, and iterate backwards so your index doesn't get out of whack.
for(var i:int=zombieCount.length-1;i >=0;i--){
zombieCount[i].y += 1; //move it down 1 pixel
if(zombieCount[i].hitTestObject(border)){
stage.removeChild(zombieCount[i]);
zombieCount.splice(i,1); //remove the item at the current index (do this instead of shift)
trace(zombieCount.length);
}
}