Flash Error #1009 - actionscript-3

Question

There's a problem with my AS3 code. The Error is:
TypeError: Error #1009: Cannot access a property or method of a null object reference.
at mcEnemy/destroyEnemy()[/Users/deorka12/Documents/School/firstGame/mcEnemy.as:94]
at firstGame/checkEnemiesOffscreen()[/Users/deorka12/Documents/School/firstGame/firstGame.as:112]
at firstGame/gameLoop()[/Users/deorka12/Documents/School/firstGame/firstGame.as:63]
And this is how my code is:
package {
import flash.display.MovieClip;
import flash.events.KeyboardEvent;
import flash.ui.Keyboard;
import flash.events.Event;
import flash.utils.Timer;
import flash.events.TimerEvent;
// public function kan je ook gebruiken in een ander as. file
// private function kan je alleen gebruiken in hetzelfde as. file
public class firstGame extends MovieClip
{
public var mcPlayer:MovieClip;
private var leftKeyIsDown:Boolean;
private var rightKeyIsDown: Boolean;
private var aMissileArray: Array;
private var aEnemyArray: Array;
public function firstGame (){
//initilaiz variables
aMissileArray = new Array ();
aEnemyArray = new Array ();
//trace("First Game Loaded");
//Listern for key presses and relesead
stage.addEventListener(KeyboardEvent.KEY_UP, keyUp);
stage.addEventListener(KeyboardEvent.KEY_DOWN, keyDown);
//Setup game event loop
stage.addEventListener(Event.ENTER_FRAME, gameLoop);
// create a timer object
var tEnemyTimer : Timer = new Timer (1000);
// listener for timer intervals
tEnemyTimer.addEventListener(TimerEvent.TIMER, addEnemy);
// start out timer
tEnemyTimer.start();
}
private function addEnemy (e:TimerEvent) : void
{
//trace ("timer ticks")
// create a new enemy object
var newEnemy:mcEnemy = new mcEnemy ();
// add object to the stage
stage.addChild (newEnemy);
// add enemy to new enemy to a new enemy array
aEnemyArray.push(newEnemy);
trace (aEnemyArray.length);
}
private function gameLoop (e:Event) : void
{
playerControl();
clampPlayerToStage();
checkMissileOffscreen();
**checkEnemiesOffscreen();**
checkMissilesHitsEnemy();
}
private function checkMissilesHitsEnemy (): void
{
// loop trough current missiles
for (var i : int = 0 ; i < aMissileArray.length; i++)
{
// get our current missile in the i loop
var currentMissile : mcMissile = aMissileArray [i];
// loop trough all our enemies
// gebruik geen i want die is al gebruikt dus j
for (var j: int = 0 ; j < aEnemyArray.length; j++)
{
// get the current enemy in the j loop
var currentEnemy: mcEnemy = aEnemyArray [j];
// test if our current enemy is hitting our current missile
if(currentMissile.hitTestObject(currentEnemy))
{
// remove the missile
currentMissile.destroyMissile();
// remove the missile from missile array
aMissileArray.splice(i, 1);
// remove the enemy from the stage
**currentEnemy.destroyEnemy();**
// remove the enemy from the enemy array
aEnemyArray.splice(j, 1);
}
}
}
}
private function checkEnemiesOffscreen (): void
{
// loop trough all our enemies
for (var i:int = 0;i < aEnemyArray.length; i++)
{
// get our current ememy in the loop
var currentEnemy: mcEnemy = aEnemyArray [i];
// when enemy moves left and is has gone past the and of the left from the stage
if (currentEnemy.sDirection == "L" && currentEnemy.x - (currentEnemy.width/2))
{
// Remove enemy from our array
aEnemyArray.slice(i,1);
// Remove enemy from stage
currentEnemy.destroyEnemy();
} else
if (currentEnemy.sDirection == "R" && currentEnemy.x > stage.stageWidth + (currentEnemy.width/2))
{
// Remove enemy from our array
aEnemyArray.slice(i,1);
// Remove enemy from stage
currentEnemy.destroyEnemy();
}
}
}
private function checkMissileOffscreen():void
{
//Loop throw all our missiles in our missle array
// i = counter object
for (var i: int = 0; i < aMissileArray.length; i++)
{
//Get the current missile in the loop
var currentMissile : mcMissile = aMissileArray [i];
//Test if current missile is out the buttom of the screen
if (currentMissile.y > 450 )
{
//Remove current missile from the array
aMissileArray.splice(i,1);
//Destroy our missile
currentMissile.destroyMissile();
}
}
}
private function clampPlayerToStage ():void
{
// if our player is to the left of the stage
if (mcPlayer.x < (mcPlayer.width/2))
{
// set our player to left of the stage
mcPlayer.x = mcPlayer.width/2;
}
// if our player is to the right of the stage
else if (mcPlayer.x > (stage.stageWidth - (mcPlayer.width/2)))
{
//set our player to right of the stage
mcPlayer.x = stage.stageWidth - (mcPlayer.width/2);
}
}
private function playerControl ():void
{
// if our left key is down currently
if (leftKeyIsDown == true)
{
//move to left
mcPlayer.x -= 5;
}
// if our right key is currently down
if (rightKeyIsDown)
{
//move to right
mcPlayer.x += 5;
}
}
private function keyUp (e:KeyboardEvent): void
{
//trace(e.keyCode)
//if your left is released
if (e.keyCode == 37)
{
//left key is released
leftKeyIsDown = false;
}
//if your right is released
if (e.keyCode == 39)
{
//right key is released
rightKeyIsDown = false;
}
//if our spacebarr is released
if (e.keyCode == 32)
{
//fire a missile
fireMissile ();
}
}
private function fireMissile ():void
{
// create a new missisile object
var newMissile : mcMissile = new mcMissile ();
// add to stage
stage.addChild(newMissile);
// position missile
newMissile.x = mcPlayer.x;
newMissile.y = mcPlayer.y;
//add our new missile to our missile array
aMissileArray.push (newMissile);
trace(aMissileArray.length)
}
private function keyDown (e:KeyboardEvent): void
{
//trace(e.keyCode)
//if your left is pressed
if (e.keyCode == 37)
{
//left key is pressed
leftKeyIsDown = true;
}
//if your right is pressed
if (e.keyCode == 39)
{
//right key is pressed
rightKeyIsDown = true;
}
}
}
}
and my other code is:
package {
import flash.display.MovieClip;
import flash.events.Event;
public class mcEnemy extends MovieClip {
public var sDirection:String;
private var nSpeed:Number;
public function mcEnemy()
{
addEventListener(Event.ADDED_TO_STAGE, onAdd);
}
private function onAdd (e:Event): void
{
removeEventListener(Event.ADDED_TO_STAGE, onAdd);
init();
}
private function init ():void
{
// 3 frames
var nEnemies:Number = 3;
// pick random number between 1 and number of enemies
var nRandom:Number = randomNumber (1, nEnemies);
// Setup our playhead of this enemy clip to a random number
// Stop op frame 1,2 of 3
this.gotoAndStop(nRandom);
// Setup our enemys start position
setupStartPosition();
}
private function setupStartPosition (): void
{
// pick a random speed for the enemy
nSpeed = randomNumber (5,10);
// Pick random number for left or right, start position
var nLeftOrRight:Number = randomNumber (1,2);
// if our nLeftOrRight == 1 , enemy is on the left
if (nLeftOrRight == 1)
{
// start enemy on the left side
this.x = - (this.width/2);
sDirection = "R";
} else
{
// start enemy on the right side
this.x = stage.stageWidth + (this.width/2);
sDirection = "L";
}
// set a random hoogte for our enemy
// set a 2 varibele for min and max hoogte
var nMinAltitude: Number = stage.stageHeight/2;
var nMaxAltitude: Number = 400 - (this.height/2);
// Setup our enemies altitude to a random point between our min and max altitudes
this.y = randomNumber (nMinAltitude, nMaxAltitude);
// move our enemy
startMoving ();
}
private function startMoving (): void
{
addEventListener(Event.ENTER_FRAME, enemyLoop)
}
private function enemyLoop (e:Event ): void
{
// test in what direction our enemy is moving
// if our enemy is moving right
if (sDirection == "R")
{
// move our enemy right
this.x += nSpeed;
} else
{
this.x -= nSpeed;
}
}
// geeft random nummer tussen 0 en 1
function randomNumber (low:Number=0, high:Number=1) : Number
{
return Math.floor (Math.random() * (1+high-low)) + low;
}
public function destroyEnemy (): void
{
// remove enemys from the stage
**parent.removeChild(this);**
// remove any eventlisteners from enemy
removeEventListener(Event.ENTER_FRAME, enemyLoop);
}
}
}
I hope someone can help me. Sorry for my bad english.

Answer 1

The error indicates that the property parent is null, meaning that your mcEnemy object has no parent. The mcEnemy object has not been added to the display list.
To fix this you can check the parent property is set first:
if(parent)
{
parent.removeChild(this);
}