我正在开展一项大学项目，在AS3中创造一个自上而下的射击游戏，我对AS3知之甚少，但仍然需要制作完成的游戏。游戏符合并运行但是当我射击敌人时我得到了这个错误
bullet hit baddie 2＆lt; ---这是一个跟踪元素
TypeError: Error #1009: Cannot access a property or method of a null object reference.
at Enemy/removeSelf()
at Bullet/loop()
at Main/loop()
非常感谢任何帮助，非常感谢。我将在下面发布我的代码，以便可以参考。
的 Main.as
package
{
import flash.display.Stage;
import flash.display.MovieClip;
import flash.events.Event;
import flash.events.MouseEvent;
public class Main extends MovieClip
{
public var player:Player;
public var enemy:Enemy;
public var bulletList:Array = [];
public var mousePressed:Boolean = false; //keeps track of whether the mouse is currently pressed down
public var delayCounter:int = 0; //this adds delay between the shots
public var delayMax:int = 7; //change this number to shoot more or less rapidly
public var enemies:Array = [];
public function Main():void
{
player = new Player(stage, 320, 240);
stage.addChild(player);
//stage.addEventListener(MouseEvent.CLICK, shootBullet, false, 0, true); //remove this
stage.addEventListener(MouseEvent.MOUSE_DOWN, mouseDownHandler, false, 0, true);
stage.addEventListener(MouseEvent.MOUSE_UP, mouseUpHandler, false, 0, true);
stage.addEventListener(Event.ENTER_FRAME, loop, false, 0, true);
for(var numBaddies=0; numBaddies<6;numBaddies++){
var enemy:Enemy = new Enemy(/*null*/);
enemy.x = numBaddies*50;
enemy.y = numBaddies*50
stage.addChild(enemy);
enemies.push(enemy);
}
}
public function loop(e:Event):void
{
if(mousePressed) // as long as the mouse is pressed...
{
delayCounter++; //increase the delayCounter by 1
if(delayCounter == delayMax) //if it reaches the max...
{
shootBullet(); //shoot a bullet
delayCounter = 0; //reset the delay counter so there is a pause between bullets
}
}
if(bulletList.length > 0)
{
for(var i:int = bulletList.length-1; i >= 0; i--)
{
bulletList[i].loop();
}
}
/*for(var h = 0; h<bulletList.length; ++h)
{
if(bulletList[h].hitTestObject(this)){
trace("player hit by baddie " + h);
}
}*/
for(var u:int=0; u<enemies.length; u++) {
Enemy(enemies[u]).moveTowards(player.x, player.y);
}
}
public function mouseDownHandler(e:MouseEvent):void //add this function
{
mousePressed = true; //set mousePressed to true
}
public function mouseUpHandler(e:MouseEvent):void //add this function
{
mousePressed = false; //reset this to false
}
public function shootBullet():void //delete the "e:MouseEvent" parameter
{
var bullet:Bullet = new Bullet(stage, player.x, player.y, player.rotation, enemies);
bullet.addEventListener(Event.REMOVED_FROM_STAGE, bulletRemoved, false, 0, true);
bulletList.push(bullet);
stage.addChild(bullet);
}
public function bulletRemoved(e:Event):void
{
e.currentTarget.removeEventListener(Event.REMOVED_FROM_STAGE, bulletRemoved);
bulletList.splice(bulletList.indexOf(e.currentTarget),1);
}
}
}
的 Enemy.as
package {
import flash.display.Stage;
import flash.display.MovieClip;
import flash.events.Event;
public class Enemy extends MovieClip {
public var bullets:Array;
public var stageRef:Stage;
private var enemyPositionX, enemyPositionY, xDistance, yDistance, myRotation:int;
public function Enemy(/*stageRef:Stage, bulletList:Array*/) {
// constructor code
/*bullets = bulletList;
this.stageRef = stageRef;*/
}
public function moveTowards(playerX:int, playerY:int){
xDistance = this.x - playerX;
yDistance = this.y - playerY;
myRotation = Math.atan2(yDistance, xDistance);
this.x -= 3 * Math.cos(myRotation);
this.y -= 3 * Math.sin(myRotation);
}
public function removeSelf():void
{
//removeEventListener(Event.ENTER_FRAME, loop);
if (stageRef.contains(this))
stageRef.removeChild(this);
}
}
}
的 Bullet.as
package
{
import flash.display.Stage;
import flash.display.MovieClip;
import flash.events.Event;
public class Bullet extends MovieClip
{
private var stageRef:Stage; //checks if the bullet leaves the screen borders
private var speed:Number = 10; //speed that the bullet will travel at
private var xVel:Number = 0; //current x velocity
private var yVel:Number = 0; //current y velocity
private var rotationInRadians = 0; //convenient to store our rotation in radians instead of degrees
public var allBaddies:Array;
//our constructor requires: the stage, the position of the bullet, and the direction the bullet should be facing
public function Bullet(stageRef:Stage, X:int, Y:int, rotationInDegrees:Number, enemies:Array):void
{
this.stageRef = stageRef;
this.x = X;
this.y = Y;
this.rotation = rotationInDegrees;
this.rotationInRadians = rotationInDegrees * Math.PI / 180; //convert degrees to radians, for trigonometry
allBaddies = enemies;
}
public function loop():void //we don't need to include the "e:Event" because we aren't using an EventListener
{
for(var b=0; b<allBaddies.length; ++b)
{
if(allBaddies[b].hitTestObject(this)){
trace("bullet hit baddie " + b);
removeSelf();
allBaddies[b].removeSelf();
}
}
xVel = Math.cos(rotationInRadians) * speed; //uses the cosine to get the xVel from the speed and rotation
yVel = Math.sin(rotationInRadians) * speed; //uses the sine to get the yVel
x += xVel; //updates the position
y += yVel;
//if the bullet goes off the edge of the screen...
if(x > stageRef.stageWidth || x < 0 || y > stageRef.stageHeight || y < 0)
{
this.parent.removeChild(this); //remove the bullet
}
}
private function removeSelf():void
{
removeEventListener(Event.ENTER_FRAME, loop);
if (stageRef.contains(this))
stageRef.removeChild(this);
}
}
}
答案 0 :(得分：1)
stageRef类中的 Enemy变量。
您正在Bullet类构造函数中传递它，但您在Enemy类中没有这样做。