Actionscript 3 error 1009: Cannot access a property or method of a null object reference - actionscript-3

Question

I'm trying to make a simple game on Animate CC. Everything seems to work fine except when I look in the output, I get the following error:
TypeError: Error #1009: Cannot access a property or method of a null
object reference.
at _2D_CW2_Game_v10_8_fla::MainTimeline/move()
at _2D_CW2_Game_v10_8_fla::MainTimeline/updateOb()
So I know where the issue might be, and I've been trying tweaking the code for days, googling possible solutions, but to no avail...
My entire source code is as below. Any feedback/suggestions will be greatly appreciated.
import flash.ui.Keyboard;
import flash.events.KeyboardEvent;
import flash.events.MouseEvent;
import flash.events.Event;
import flash.display.MovieClip;
import flash.net.URLRequest;
import flash.media.Sound;
import flash.media.SoundMixer;
//==================================================
// Variable declaration
//==================================================
// defines the variables for boundaries
var left:Number = 0;
var top:Number = 0;
var right:Number = stage.stageWidth;
var bottom:Number = stage.stageHeight;
var velX:Number = 0;
var velY:Number = 0;
var gravity:Number = 1;
var friction:Number = 0.8;
var bounce:Number = -0.5;
var score:Number = 2;
var cv:Number = 0;
var curCount:Number = 30; // countdown 30s
var rightKeyDown:Boolean = false;
var leftKeyDown:Boolean = false;
var upKeyDown:Boolean = false;
var touchGround:Boolean = false;
// create and place player object on stage
var player:Player = new Player();
player.x = 110;
player.y = 460;
addChild(player);
// create obstacle array
var obstacles:Array = new Array();
var numOb:Number = 3;
// create and place enemies on stage
for (var i:Number = 0; i < numOb; i++) {
var ob:Npc = new Npc();
ob.x = 800;
ob.y = 470;
ob.scaleX = -1;
ob.vx = Math.random() * 20 + 1;
addChild(ob);
obstacles.push(ob);
}
//==================================================
// Event handlers
//==================================================
stage.addEventListener(Event.ENTER_FRAME, EntFrame);
addEventListener(Event.ENTER_FRAME, updateOb);
stage.addEventListener(KeyboardEvent.KEY_DOWN, keyDown);
stage.addEventListener(KeyboardEvent.KEY_UP, keyUp);
//==================================================
// Functions
//==================================================
function keyDown(e:KeyboardEvent):void {
if (e.keyCode == Keyboard.RIGHT) {
rightKeyDown = true;
}
if (e.keyCode == Keyboard.LEFT) {
leftKeyDown = true;
}
if (e.keyCode == Keyboard.UP) {
// if player isn't already jumping and is on the ground
if (!upKeyDown && touchGround) {
// then start jumping
isJumping();
}
upKeyDown = true;
}
}
function keyUp(e:KeyboardEvent):void {
if (e.keyCode == Keyboard.RIGHT) {
rightKeyDown = false;
}
if (e.keyCode == Keyboard.LEFT) {
leftKeyDown = false;
}
if (e.keyCode == Keyboard.UP) {
upKeyDown = false;
}
}
function EntFrame(e:Event):void {
player.x += velX;
player.y += velY;
velX *= friction;
velY += gravity;
if (player.y >= 450) {
touchGround = true;
player.y = 450;
}
// boundary checks
if (player.x + player.width/2 > right) {
player.x = right - player.width/2;
player.velX *= bounce;
} else if (player.x - player.width/2 < left) {
player.x = left + player.width/2;
player.velX *= bounce;
}
// make player move left or right
controls();
if (curCount > 0) {
cv++;
if (cv >= 30) {
curCount--;
cv = 0;
timertext.text = String(curCount);
if (curCount == 0) {
restart();
gotoAndStop("gameOverWon");
}
}
}
}
function updateOb(e:Event):void {
// make obstacles move
for (var i:Number = 0; i < numOb; i++) {
var ob:Npc = obstacles[i];
move(ob);
if (player.hitTestObject(obstacles[i])) {
/*if (obstacles[i].hitTestPoint(player.x + player.width/2, player.y + player.height/2, true)
|| obstacles[i].hitTestPoint(player.x + player.width/2, player.y - player.height/2, true)
|| obstacles[i].hitTestPoint(player.x - player.width/2, player.y + player.height/2, true)
|| obstacles[i].hitTestPoint(player.x - player.width/2, player.y - player.height/2, true))*/
bumpOb(obstacles[i]);
}
}
scoretext.text = String(score);
if (score == 0) {
restart();
gotoAndStop("gameOverLost");
}
}
// applies basic velocity to enemies
function move(moveOb) {
moveOb.x -= moveOb.vx;
if (moveOb.x + moveOb.width/2 > right) {
moveOb.x = right - moveOb.width/2;
moveOb.vx *= bounce;
moveOb.scaleX = -1;
}
if (moveOb.x - moveOb.width/2 < left) {
moveOb.x = left + moveOb.width/2;
moveOb.vx *= bounce;
moveOb.scaleX = 1;
}
}
function bumpOb(p) {
if (p) {
p.removeEventListener(Event.ENTER_FRAME, updateOb);
if (p.parent) {
removeChild(p);
score--;
}
}
}
function restart() {
if(contains(player)) {
removeChild(player);
}
for (var i:int = 0; i < numOb; i++) {
if (contains(obstacles[i]) && obstacles[i] != null) {
removeChild(obstacles[i]);
obstacles[i] = null;
}
}
// returns a new array that consists of a range of elements from the original array,
// without modifying the original array
obstacles.slice(0);
}
function controls() {
if (rightKeyDown) {
velX += 3;
player.scaleX = 1;
}
if (leftKeyDown) {
velX -= 3;
player.scaleX = -1;
}
}
function isJumping() {
touchGround = false;
velY = -15;
}
//==================================================
// Sound control for background music
//==================================================
btnMute.addEventListener(MouseEvent.CLICK, mute);
function mute(e:MouseEvent):void {
SoundMixer.soundTransform = new SoundTransform(0);
btnMute.removeEventListener(MouseEvent.CLICK, mute);
btnMute.addEventListener(MouseEvent.CLICK, unmute);
}
function unmute(e:MouseEvent):void {
SoundMixer.soundTransform = new SoundTransform(1);
btnMute.removeEventListener(MouseEvent.CLICK, unmute);
btnMute.addEventListener(MouseEvent.CLICK, mute);
}

Answer 1

I had the same problem when I created interactive elements for animation. Check which layer the interactive object is on. A similar error occurred when the object overlapped something that was located on the layer above.

Answer 2

You can try...
1) Your Npc is a class/library object, right?
Give the source MC/Sprite, the instance name of moveOb or p.
2) or else try... Use function parameters (this is a better coding style):
(2a) Since you say..
var ob:Npc = obstacles[i];
move(ob);
ps: why not simplify (without var) as : move( obstacles[i] ); ...?
(2b) Your move function should specify a data type together with your parameter name...
//# applies basic velocity to enemies
//# Wrong...
//function move(moveOb) {
//# Better...
function move( moveOb : Npc ) {
//# Aso fix as...
function bumpOb(p : Npc ) {
By using function parameters, you can now give unique names to the (function's) input parameters but stay referencing the same (or compatible) data type.
Let me know how it goes.

Answer 3

The obstacles array may have null elements in the middle. What if you add a condition to continue if it's null?
function updateOb(e:Event):void {
// make obstacles move
for (var i:Number = 0; i < obstacles.length; i++) {
var ob:Npc = obstacles[i];
if(!ob) continue;
move(ob);
if (player.hitTestObject(ob)) {
/*if (obstacles[i].hitTestPoint(player.x + player.width/2, player.y +
player.height/2, true)
|| obstacles[i].hitTestPoint(player.x + player.width/2, player.y -
player.height/2, true)
|| obstacles[i].hitTestPoint(player.x - player.width/2, player.y +
player.height/2, true)
|| obstacles[i].hitTestPoint(player.x - player.width/2, player.y -
player.height/2, true))*/
bumpOb(obstacles[i]);
}
}
scoretext.text = String(score);
if (score == 0) {
restart();
gotoAndStop("gameOverLost");
}
}