Flash - Adding objects to a scene randomly, at certain set points - actionscript-3

Question

I'm in the process of creating a simple Flash game using ActionScript 3.0 and have come across an issue when spawning my obstacles onto the scene. My aim is to have approximately 10 points across the x axis (remaining at the same y axis) and when spawning the obstacles into my scene it will pick 2-4 of those points randomly and spawn them on them.
I've got the obstacles to spawn randomly but cannot figure out how to make them spawn at random set points, from a list. If anyone could help, I would be much appreciative. Thanks
EDIT:
The code I have so far:
var a:Array = new Array();
for (var count=0; count< 5; count++) {
a[count] = new asteroidOne();
a[count].x = 100 * count + (Math.floor(Math.random() * 200));
a[count].y = 100;
addChild(a[count]);
}
// Asteroid obstacle spawning 2.0
player.addEventListener(Event.ENTER_FRAME, obstacleMove);
function obstacleMove(evt:Event):void {
for (var i=0; i< 5; i++) {
a[i].y += 5;
if (a[i].y == 480) {
a[i].y = 0;
}
if (player.hitTestObject(a[i])) {
trace("HIT");
}
}
}

Answer 1

Assuming you have your spawn points in an array, you could do the following:
var spawnPoints:Array = [100,200,250,300,450,500,600,800]; //your list of spawn x locations
spawnPoints.sort(randomizeArray); //lets randomize the spwanPoints
function randomizeArray(a:*, b:*):int {
return ( Math.random() < .5 ) ? 1 : -1;
}
var a:Vector.<asteroidOne> = new Vector.<asteroidOne>(); //the array for your astroids - changed to vector for possible performance and code hint improvement (basically the same as Array but every object has to be of the specified type)
for (var count:int=0; count < 5; count++) {
a.push(new asteroidOne());
a[count].x = spawnPoints.pop(); //pop removes the last element from the array and returns it
a[count].y = 100;
addChild(a[count]);
}
EDIT
To address you comments, here is a decent example:
import flash.events.Event;
import flash.events.TimerEvent;
import flash.utils.Timer;
var spawnTimer:Timer = new Timer(10000); //timer will tick every 10 seconds
spawnTimer.addEventListener(TimerEvent.TIMER, spawn, false, 0, true); //let's run the spawn function every timer tick
spawnTimer.start();
var spawnPoints:Array = [100,200,250,300,450,500,600,800]; //your list of spawn x locations
var spawnAmount:int = 5; //how many asteroids to have on the screen at once (you could increase this over time to make it more difficult)
var asteroids:Vector.<asteroidOne> = new Vector.<asteroidOne>(); //the array for your asteroids - changed to vector for possible performance and code hint improvement (basically the same as Array but every object has to be of the specified type)
spawn(); //lets call it right away (otherwise it will won't be called until the first timer tick in 10 seconds)
//calling this will spawn as many new asteroids as are needed to reach the given amount
function spawn(e:Event = null):void {
if(asteroids.length >= spawnAmount) return; //let's not bother running any of the code below if no new asteroids are needed
spawnPoints.sort(randomizeArray); //lets randomize the spwanPoints
var spawnIndex:int = 0;
var a:asteroidOne; //var to hold the asteroid every loop
while (asteroids.length < spawnAmount) {
a = new asteroidOne();
a.x = spawnPoints[spawnIndex];
spawnIndex++; //incriment the spawn index
if (spawnIndex >= spawnPoints.length) spawnIndex = 0; //if the index is out of range of the amount of items in the array, go back to the start
a.y = 100;
asteroids.push(a); //add it to the array/vector
addChild(a); //add it to the display
}
}
player.addEventListener(Event.ENTER_FRAME, obstacleMove);
function obstacleMove(evt:Event):void {
//this is the same as a backwards for loop - for(var i:int=asteroids.length-1;i >= 0; i--)
var i:int = asteroids.length;
while(i--){ //since we are potentially removing items from the array/vector, we need to iterate backwards - otherwise when you remove an item, the indices will have shifted and you'll eventually get an out of range error
asteroids[i].y += 5;
if (asteroids[i].y > stage.stageHeight || asteroids[i].x > stage.stageWidth || asteroids[i].x < -asteroids[i].width || asteroids[i].y < -asteroids[i].height) {
//object is out of the bounds of the stage, let's remove it
removeChild(asteroids[i]); //remove it from the display
asteroids.splice(i, 1); //remove it from the array/vector
continue; //move on to the next iteration in the for loop
}
if (player.hitTestObject(asteroids[i])) {
trace("HIT");
}
}
}
function randomizeArray(a:*, b:*):int {
return ( Math.random() < .5 ) ? 1 : -1;
}