AS3-Flash Pro CS6-無法訪問空對象引用的屬性或方法

Question

我正在做一個大學項目，以在AS3中創建自上而下的射擊游戲，我對AS3知之甚少，但仍然必須制作完成的游戲。 游戲運行並運行，但是當我射擊敵人時出現此錯誤

bullet hit baddie 2 <---這是微量元素
TypeError: Error #1009: Cannot access a property or method of a null object reference.
at Enemy/removeSelf()
at Bullet/loop()
at Main/loop()

非常感謝任何幫助，非常感謝。 我將在下面發布我的代碼，以便可以對其進行引用。


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);
    }
}
}

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);
    }
}

}

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);
    }
}
}

Answer 1

永遠不會設置Enemy類中的stageRef變量。 您正在Bullet類構造函數中傳遞它，但在Enemy類中卻沒有這樣做。