我使用AS3在Flash CS6上制作了一款游戏。游戏在屏幕的右侧有一个宇宙飞船，它会向外星人射出子弹，随机出现在右侧。游戏完全正常，但是当我玩它的时候我偶然会遇到这个错误。
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]
现在这里是外星人3的AS链接
包{
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;
}
}
}
因此第43行响应图书馆中的外星导弹电影剪辑 parent.addChild（AO）;
这很奇怪，因为它可以毫无问题地添加外星导弹并且工作正常 alienMissile3是一个影片剪辑，它被转换为一个名为不同的png的影片剪辑。
我不知道导致此错误的原因。
主时间轴中的代码如下。
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);
}
}
答案 0 :(得分：0)
您收到错误是因为您在检查Alien3的父级之前已将其添加到显示列表中。
在parent.addChild（ao）行之前添加一条跟踪，即：
trace("Alien3 parent = "+parent);
我打赌输出有时会为空。
解决方案是使用ADDED_TO_STAGE事件侦听器替换ENTER_FRAME事件侦听器（在Alien3构造函数中）。试试这个：
public function alien3() {
addEventListener(Event.ADDED_TO_STAGE, onStage);
}
private function onStage(e:Event):void {
removeEventListener(Event.ADDED_TO_STAGE, onStage);
addEventListener(Event.ENTER_FRAME, pulse);
}
现在，当调用脉冲时，“父母”＃39;不会为null，因为该实例位于显示列表中，并且可以访问“父母”。