Ошибка #1009 иногда во время игры

Я сделал игру на Flash CS6 с использованием AS3. В игре есть космический корабль в правой части экрана, и он стреляет пулями в инопланетян, которые случайным образом появляются справа. Игра работает отлично, но время от времени, когда я играю в нее, я получаю эту ошибку.

TypeError: Error #1009: Cannot access a property or method of a null object reference.
at alien3/pulse()[/Users/Matt/Documents/DES B Assignment/Prototype/alien3.as:43]

Теперь вот связь AS для пришельца 3

упаковка {

import flash.display.MovieClip;
import flash.events.Event;


public class alien3 extends MovieClip {

    var yMove:Number = 15;
    var changeDirectionAfterYMoves:Number = 0;
    var moveCount:Number = 0;

    var shootCount:Number = 0;
    var shootMissilesAfterYMoves:Number = 0;

    public function alien3() {
        addEventListener(Event.ENTER_FRAME,pulse);
    }

    public function stopListening() 
    {
        removeEventListener(Event.ENTER_FRAME,pulse);
    }

    public function pulse(evt:Event)
    {
        if (currentFrame!=1) return;
        if(changeDirectionAfterYMoves == moveCount)
        {
            yMove=yMove*-1;
            var maxMoves:Number;
            if (yMove>0)maxMoves = Math.round (400-this.y)/yMove;
            else maxMoves = Math.round((this.y)/Math.abs(yMove));
            changeDirectionAfterYMoves = 1 + Math.round (Math.random () *maxMoves);
            moveCount = 0;  
        }

        if (shootCount==shootMissilesAfterYMoves)
        {
            var ao:alienMissile3 = new alienMissile3 ();
            ao.x = this.x + 50;
            ao.y = this.y;
            parent.addChild(ao);
            shootCount=0;
            shootMissilesAfterYMoves = 1 + Math.round (Math.random() * 25)
        }

        this.y+=yMove;
        moveCount = moveCount+1;
        shootCount = shootCount+1;

        }

    }
}

Таким образом, строка 43 отвечает на видеоклип с инопланетной ракетой в библиотеке parent.addChild(ao);

Что странно, потому что он без проблем добавляет инопланетные ракеты, и они работают нормально. AlienMissile3 — это муви-клип, который был преобразован в муви-клип из png с другим названием.

Я понятия не имею, что вызывает эту ошибку.

Код на основной временной шкале выглядит следующим образом.

    import flash.display.MovieClip;
import flash.events.Event;
import flash.media.SoundChannel;
import flash.net.dns.AAAARecord;


var frameCount:Number = 0;
var alienCount:Number = 0;
var alienInterval:Number = 100;
var score:Number=0;
var gameOn:Boolean = false
var my_sound:laserGun = new laserGun();
var my_channel:SoundChannel = new SoundChannel();
var my_sound3:QueenAmidalaandTheNabooPalace = new QueenAmidalaandTheNabooPalace();
var my_channel3:SoundChannel = new SoundChannel();
var spaceshipMovement:Number = 0;


mcGameOverScreen.visible=false;

var scoresArray:Array = new Array();

var SO:SharedObject = SharedObject.getLocal("scores5");

if (SO.size!=0)
{
    scoresArray = SO.data.scoresArray;
}

function startGame()
{
    addEventListener(Event.ENTER_FRAME, pulse);
    gameOn=true;
    mySpaceship.livesLeft=3;
    score=0;
}


function pulse(event:Event):void
{   

    if (mySpaceship.livesLeft<1) noLivesLeft();
    addNewAlienIfNecessary();
    /*addNewAlien2IfNecessary();
    addNewAlien3IfNecessary();*/

    checkForMissileOnAlien();
    checkForMissileOnAlien2();
    checkForMissileOnAlien3();

    checkForMissileOnAlienMissile();
    checkForMissileOnAlienMissile2();
    checkForMissileOnAlienMissile3();

    tidyUp();

    checkForAlienMissileOnSpaceship();
    checkForAlienMissile2OnSpaceship();
    checkForAlienMissile3OnSpaceship();

    tbScore.text = String(score);
    tbLivesLeft.text = String (mySpaceship.livesLeft);

    var bg:background = new background();
    bg.y = 0;
    bg.x = 0;
    addChild(bg);
    gameOn=true;

}

function addNewAlienIfNecessary()
{
    if (score<=100 && alienCount<3 && frameCount%60==0)
    {
        var a:alien = new alien();
        a.x = Math.random()*380;
        a.y = Math.random()*50;
        addChild(a);
        alienCount=alienCount+1;

    }
    //frameCount++;


    if (score >100 && score<500 && alienCount<3 && frameCount%80==0)
    {
        var aa:alien2 = new alien2();
        aa.x = Math.random()*380;
        aa.y = Math.random()*50;
        addChild(aa);
        alienCount=alienCount+1;

    }
    //frameCount++;

    if (alienCount<3 && score>=500 && frameCount%100==0)
    {
        var ab:alien3 = new alien3();
        ab.x = Math.random()*380;
        ab.y = Math.random()*50;
        addChild(ab);
        alienCount=alienCount+1;
    }
    frameCount++;

}

/*function addNewAlien2IfNecessary()
{
    if (score>100 && score<500 && alienCount<3 && frameCount%60==0)
    {
        var aa:alien2 = new alien2();
        aa.x = Math.random()*440;
        aa.y = Math.random()*50;
        addChild(aa);
        alienCount=alienCount+1;
    }
    frameCount++;
}

function addNewAlien3IfNecessary()
{
    if (score>500 && alienCount<3 && frameCount%60==0)
    {
        var ab:alien3 = new alien3();
        ab.x = Math.random()*440;
        ab.y = Math.random()*50;
        addChild(ab);
        alienCount=alienCount+1;
    }
    frameCount++;
}*/


function checkForMissileOnAlien()
{
    var missilez:Array = new Array;
    var alienz:Array = new Array;

    for (var i=0;i<numChildren;i++)
    {
        if (getChildAt(i) is alien) {alienz.push(getChildAt(i) as MovieClip)};
        if (getChildAt(i) is missile) {missilez.push(getChildAt(i) as MovieClip)};
    }

    for (var j=0;j<alienz.length;j++)
    {
        for (var k=0;k<missilez.length;k++)
            {
                if (alienz[j].hitTestObject(missilez[k]))
                    {
                        alienz[j].gotoAndStop (2);
                        //alienz[j].stopListening();
                        missilez[k].gotoAndStop(2);
                        missilez[k].stopListening();

                        var e:explosion = new explosion();
                        e.x = alienz[j].x;
                        e.y = alienz[j].y;
                        addChild(e);

                        alienCount = alienCount-1;
                        score += 20;
                    }
            }
    }

}

function checkForMissileOnAlien2()
{
    var missilez:Array = new Array;
    var alienz2:Array = new Array;

    for (var i=0;i<numChildren;i++)
    {
        if (getChildAt(i) is alien2) {alienz2.push(getChildAt(i) as MovieClip)};
        if (getChildAt(i) is missile) {missilez.push(getChildAt(i) as MovieClip)};
    }

    for (var j=0;j<alienz2.length;j++)
    {
        for (var k=0;k<missilez.length;k++)
            {
                if (alienz2[j].hitTestObject(missilez[k]))
                    {
                        alienz2[j].gotoAndStop (2);
                        //alienz2[j].stopListening();
                        missilez[k].gotoAndStop(2);
                        missilez[k].stopListening();

                        var e:explosion = new explosion();
                        e.x = alienz2[j].x;
                        e.y = alienz2[j].y;
                        addChild(e);

                        alienCount = alienCount-1;
                        score += 50;
                    }
            }
    }

}

function checkForMissileOnAlien3()
{
    var missilez:Array = new Array;
    var alienz3:Array = new Array;

    for (var i=0;i<numChildren;i++)
    {
        if (getChildAt(i) is alien3) {alienz3.push(getChildAt(i) as MovieClip)};
        if (getChildAt(i) is missile) {missilez.push(getChildAt(i) as MovieClip)};
    }

    for (var j=0;j<alienz3.length;j++)
    {
        for (var k=0;k<missilez.length;k++)
            {
                if (alienz3[j].hitTestObject(missilez[k]))
                    {
                        alienz3[j].gotoAndStop (2);
                        //alienz3[j].stopListening();
                        missilez[k].gotoAndStop(2);
                        missilez[k].stopListening();

                        var e:explosion = new explosion();
                        e.x = alienz3[j].x;
                        e.y = alienz3[j].y;
                        addChild(e);

                        alienCount = alienCount-1;
                        score += 100;
                    }
            }
    }

}

function checkForMissileOnAlienMissile()
{
    var alienMissilez:Array = new Array();
    var missilez:Array = new Array();

    for (var i=0;i<numChildren;i++)
    {
        if (getChildAt(i) is alienMissile) {alienMissilez.push(getChildAt(i) as MovieClip);}
        if (getChildAt(i) is missile) {missilez.push(getChildAt(i) as MovieClip);}
    }

    trace("alienMissilez" + alienMissilez.length);
    trace("missilez" + missilez.length);

    for (var j=0;j<alienMissilez.length;j++)
        {
            for (var k=0;k<missilez.length;k++)
            {
                if (alienMissilez[j].hitTestObject(missilez[k]))
                    {
                        alienMissilez[j].gotoAndPlay(2);
                        alienMissilez[j].stopListening();

                        missilez[k].gotoAndPlay(2);
                        missilez[k].stopListening();

                        var e:explosion = new explosion();
                        e.x = alienMissilez[j].x;
                        e.y = alienMissilez[j].y;
                        addChild(e);
                        score += 10;

                    }
            }
        }

}

function checkForMissileOnAlienMissile2()
{
    var alienMissilez2:Array = new Array();
    var missilez:Array = new Array();

    for (var i=0;i<numChildren;i++)
    {
        if (getChildAt(i) is alienMissile2) {alienMissilez2.push(getChildAt(i) as MovieClip);}
        if (getChildAt(i) is missile) {missilez.push(getChildAt(i) as MovieClip);}
    }

    trace("alienMissilez2" + alienMissilez2.length);
    trace("missilez" + missilez.length);

    for (var j=0;j<alienMissilez2.length;j++)
        {
            for (var k=0;k<missilez.length;k++)
            {
                if (alienMissilez2[j].hitTestObject(missilez[k]))
                    {
                        alienMissilez2[j].gotoAndPlay(2);
                        alienMissilez2[j].stopListening();

                        missilez[k].gotoAndPlay(2);
                        missilez[k].stopListening();

                        var e:explosion = new explosion();
                        e.x = alienMissilez2[j].x;
                        e.y = alienMissilez2[j].y;
                        addChild(e);
                        score += 15;

                    }
            }
        }

}

function checkForMissileOnAlienMissile3()
{
    var alienMissilez3:Array = new Array();
    var missilez:Array = new Array();

    for (var i=0;i<numChildren;i++)
    {
        if (getChildAt(i) is alienMissile3) {alienMissilez3.push(getChildAt(i) as MovieClip);}
        if (getChildAt(i) is missile) {missilez.push(getChildAt(i) as MovieClip);}
    }

    trace("alienMissilez3" + alienMissilez3.length);
    trace("missilez" + missilez.length);

    for (var j=0;j<alienMissilez3.length;j++)
        {
            for (var k=0;k<missilez.length;k++)
            {
                if (alienMissilez3[j].hitTestObject(missilez[k]))
                    {
                        alienMissilez3[j].gotoAndPlay(2);
                        alienMissilez3[j].stopListening();

                        missilez[k].gotoAndPlay(2);
                        missilez[k].stopListening();

                        var e:explosion = new explosion();
                        e.x = alienMissilez3[j].x;
                        e.y = alienMissilez3[j].y;
                        addChild(e);
                        score += 20;

                    }
            }
        }

}



/*function tidyUp()
{
    for (var j=numChildren-1;j>=0;j--)
    {
        if (getChildAt(j) is TextField) continue; //This added to help text box work
        var mc:MovieClip = getChildAt(j) as MovieClip;
        if (getChildAt(j) is explosion) 
        {
            if (mc.currentFrame==15) removeChildAt(j);
            continue;
        }

        //if (mc.x>800 ||  mc.x<0 || mc.currentFrame!=1  ) removeChildAt(j);
    }
}
*/

function tidyUp()
{
    for (var j=numChildren-1;j>=0;j--)
    {
        if (getChildAt(j) is TextField) continue;
        if (getChildAt(j) is SimpleButton) continue;
        var mc:MovieClip = getChildAt(j) as MovieClip;

        if (getChildAt(j) is explosion) 
        {
            if (mc.currentFrame==10) removeChildAt(j);
            //continue;
        }

        if (getChildAt(j) is alienMissile)
        {
            if (mc.x>800||(mc.currentFrame==10)) removeChildAt(j);
            //continue;
        }

        if (getChildAt(j) is alienMissile2)
        {
            if (mc.x>800||(mc.currentFrame==10)) removeChildAt(j);
            //continue;
        }

        if (getChildAt(j) is alienMissile3)
        {
            if (mc.x>800||(mc.currentFrame==10)) removeChildAt(j);
            //continue;
        }

        if(getChildAt(j) is missile)
        {
            if(mc.x<0||(mc.currentFrame==2)) removeChildAt(j);
            //continue;
        }

        if(getChildAt(j) is alien)
        {
            if(mc.currentFrame!=1) removeChildAt(j);
            //continue;
        }

        if(getChildAt(j) is alien2)
        {
            if(mc.currentFrame!=1) removeChildAt(j);
            //continue;
        }

        if(getChildAt(j) is alien3)
        {
            if(mc.currentFrame!=1) removeChildAt(j);
            //continue;
        }

    }
}

function checkForAlienMissileOnSpaceship()
{
    for (var i=0;i<numChildren;i++)
    {
        if (getChildAt(i) is alienMissile)
        {
            if (getChildAt(i).hitTestObject(mySpaceship))
            {
                var mc:MovieClip = getChildAt(i) as MovieClip;
                if (mc.currentFrame==1) 
                {
                    mc.gotoAndPlay(2);
                    mc.stopListening();
                    var e:explosion = new explosion();
                    e.x = mc.x;
                    e.y = mc.y;
                    addChild(e);
                    mySpaceship.isHit();
                }
            }
        }
    }
}   

function checkForAlienMissile2OnSpaceship()
{
    for (var i=0;i<numChildren;i++)
    {
        if (getChildAt(i) is alienMissile2)
        {
            if (getChildAt(i).hitTestObject(mySpaceship))
            {
                var mc:MovieClip = getChildAt(i) as MovieClip;
                if (mc.currentFrame==1) 
                {
                    mc.gotoAndPlay(2);
                    mc.stopListening();
                    var e:explosion = new explosion();
                    e.x = mc.x;
                    e.y = mc.y;
                    addChild(e);
                    mySpaceship.isHit();
                }
            }
        }
    }
}   

function checkForAlienMissile3OnSpaceship()
{
    for (var i=0;i<numChildren;i++)
    {
        if (getChildAt(i) is alienMissile3)
        {
            if (getChildAt(i).hitTestObject(mySpaceship))
            {
                var mc:MovieClip = getChildAt(i) as MovieClip;
                if (mc.currentFrame==1) 
                {
                    mc.gotoAndPlay(2);
                    mc.stopListening();
                    var e:explosion = new explosion();
                    e.x = mc.x;
                    e.y = mc.y;
                    addChild(e);
                    mySpaceship.isHit();
                }
            }
        }
    }
}   

stage.addEventListener (KeyboardEvent.KEY_DOWN, spaceshipControls);

function spaceshipControls (event:KeyboardEvent):void
    {
        if (event.keyCode==38 && mySpaceship.y>+62 && stage.frameRate==24) {mySpaceship.y-=20;}
        if (event.keyCode==40 && mySpaceship.y<480-mySpaceship.height && stage.frameRate==24) {mySpaceship.y+=20;}

        if (event.keyCode==32 && gameOn==true && stage.frameRate==24) 
        {
            var m:missile = new missile();
            m.y = mySpaceship.y;
            m.x = mySpaceship.x - 80;
            addChild(m);
            my_channel = my_sound.play();
        }

    }

btn_up.addEventListener(MouseEvent.MOUSE_DOWN, goUp);
btn_up.addEventListener(MouseEvent.MOUSE_UP, stopMoving);

function goUp(evt:MouseEvent)
{
    if (mySpaceship.y>+62 && stage.frameRate==24) 
        {
            mySpaceship.y-=20;
        } 
    else 
        {
            spaceshipMovement=0;
        }

}

function stopMoving (evt:MouseEvent)
{                    
    spaceshipMovement=0;
}


btn_down.addEventListener(MouseEvent.MOUSE_DOWN, goDown);
btn_down.addEventListener(MouseEvent.MOUSE_UP, stopMoving2);

function goDown(evt:MouseEvent)
{
    if (mySpaceship.y<480-mySpaceship.height && stage.frameRate==24) 
    {
    mySpaceship.y+=20;
    } 
    else 
    {
    spaceshipMovement=0;
    }

}

function stopMoving2 (evt:MouseEvent)
{                    
    spaceshipMovement=0;     
}

btn_fire.addEventListener(MouseEvent.MOUSE_DOWN, fire);

function fire(evt:MouseEvent)
{
    var m:missile = new missile();
    m.y = mySpaceship.y;
    m.x = mySpaceship.x - 80;
    addChild(m);
    my_channel = my_sound.play();
}

function noLivesLeft()
{
    stage.removeEventListener(KeyboardEvent.KEY_DOWN, spaceshipControls);
    btn_fire.removeEventListener(MouseEvent.MOUSE_DOWN, fire);
    flash.media.SoundMixer.stopAll();
    my_channel3 = my_sound3.play();
    removeEventListener(Event.ENTER_FRAME,pulse);
    for (var i=0;i<numChildren;i++)
    {

        //trace(i);
        if (getChildAt(i) is TextField) continue;
        if (getChildAt(i) is SimpleButton) continue;
        var mc:MovieClip = getChildAt(i) as MovieClip;
        if (mc.hasEventListener(Event.ENTER_FRAME)) mc.stopListening();
    }
    gameOn = false;
    mcGameOverScreen.visible = true;
    mcGameOverScreen.tb_score.text =  String (score);
    stage.removeEventListener(KeyboardEvent.KEY_DOWN, spaceshipControls);
    btn_fire.removeEventListener(MouseEvent.MOUSE_DOWN, fire);

    for (var c=numChildren-1;c>=0;c--)
    {
        var d = getChildAt(c);
        if (d is alien || d is alienMissile|| d is explosion || d is missile || d is  alien2 || d is alien3 ||d is alienMissile2 ||d is alienMissile3 || d is background)    removeChildAt(c);
    }


     }


    btnResume.addEventListener(MouseEvent.MOUSE_DOWN, resumeGame);

    function resumeGame(e:MouseEvent):void
    {
     stage.frameRate = 24
     btnPause.visible=true;
     btnResume.visible=false;
     }

     btnPause.addEventListener(MouseEvent.MOUSE_DOWN, pauseGame);

     function pauseGame(e:MouseEvent):void
     {
     stage.frameRate = 0
     btnPause.visible=false;
     btnResume.visible=true;
     }


    function setMute(vol)
    {
    var sTransform:SoundTransform = new SoundTransform(1,0);
    sTransform.volume = vol;
    SoundMixer.soundTransform = sTransform;
    }
    var isMuted:Boolean = false;
     muteBtn.addEventListener(MouseEvent.CLICK,toggleMuteBtn);
     function toggleMuteBtn(event:Event){
      if(isMuted)
     {
          isMuted = false;
          setMute(1);
     }
     else
     {
          isMuted = true;
          setMute(0);
     }
     }