AS3 - removeEventListener(ADDED_TO_STAGE)

Posted 2023-02-18

【中文标题】AS3 - removeEventListener(ADDED_TO_STAGE)

【英文标题】：

【发布时间】：2012-11-08 18:21:53

【问题描述】：

我在尝试删除 Event.ADD_TO_STAGE 时遇到了一些问题，基本上在我开发的这个游戏中，一旦生命小于或等于零，游戏将结束并切换到屏幕上的游戏，但是当我这样做时它会踢返回此错误。

ArgumentError: Error #2025: The supplied DisplayObject must be a child of the caller.   
at flash.display::DisplayObjectContainer/removeChild()
at States/changeState()
at AvoiderGame/onTick()
at flash.utils::Timer/_timerDispatch()
at flash.utils::Timer/tick()

然后变成..

TypeError: Error #1009: Cannot access a property or method of a null object reference.
at Enemy/StayOnScreen()
at AvoiderGame/onTick()
at flash.utils::Timer/_timerDispatch()
at flash.utils::Timer/tick()

我不完全确定为什么 - 谁能澄清它为什么会这样以及我该如何解决它？

package

import flash.display.MovieClip;
import flash.utils.Timer;
import flash.events.Event;
import flash.events.TimerEvent;
import com.freeactionscript.CollisionTest;
import flash.display.Stage;

public class AvoiderGame extends MovieClip

    var theCallBackFunction:Function;

    public static var enemyArray:Array;
    public var enemy:Enemy
    public var Background:gameBackground;
    public var Lives:Number = 3;

    public var avatar:Avatar;
    public var gameTimer:Timer;

    private var _collisionTest:CollisionTest;
    private var numStars:int = 80;

    private var fireTimer:Timer; //causes delay between fires
    private var canFire:Boolean = true; //can you fire a laser

    public function AvoiderGame(callBack)
    
        this.addEventListener(Event.ADDED_TO_STAGE, init);
        theCallBackFunction = callBack;
    

    private function init(e:Event):void
    
        Background = new gameBackground();
        addChild(Background);

        enemyArray = new Array();

        avatar = new Avatar(stage);
        addChild(avatar);

        avatar.x = stage.stageWidth / 2;
        avatar.y = stage.stageHeight / 2;

        _collisionTest = new CollisionTest();

        gameTimer = new Timer(25);
        gameTimer.addEventListener(TimerEvent.TIMER, onTick);
        gameTimer.start();

        for (var i:int = 0; i < numStars; i++)
        
            stage.addChildAt(new Star(stage), 1);
        

        fireTimer = new Timer(1000, 1);
        fireTimer.addEventListener(TimerEvent.TIMER, fireTimerHandler, false, 0, true);
        fireTimer.start();
    

    public function onTick(timerEvent:TimerEvent):void 
    

        if (Math.random() < 0.1)
        
            trace('array length: ', AvoiderGame.enemyArray.length);
            enemy = new Enemy(Math.round(1 + (500 - 1) * Math.random()), - 28, stage);
            enemyArray.push(enemy);
            addChild(enemy);
            enemy.gotoAndStop("Enemy" + Math.round(1 + (5 - 1) * Math.random()))
        

        canFire = avatar.UpdateAvatar(canFire);
        if (canFire == false)
        
            fireTimer.start();
        
        avatar.StayOnScreen();

        for each (var enemy:Enemy in enemyArray)
        
            enemy.moveDown();
            enemy.StayOnScreen();
            if (_collisionTest.complex(enemy, avatar)) 
            
                gameTimer.stop();
                for each (var enemy:Enemy in enemyArray)
                
                    for(var i:int = 0; i < enemyArray.length; i++)
                    
                        removeChild(enemyArray[i]);
                        enemyArray.splice(i, 1); //remove the i'th element as i'th element is the enemy containing the ID of hit enemy
                    
                
                Lives--;
                trace('lives: ', Lives);
                gameTimer.start();
            
        

        if (Lives == 0)
        
            removeEventListener(Event.ADDED_TO_STAGE, init)
            theCallBackFunction(this, "over");
        
    
    private function fireTimerHandler(e:TimerEvent) : void
    
        //timer ran, we can fire again.
        canFire = true;
    

【问题讨论】：

onTick 在哪里 - 你得到了错误？同样在 ADDED_TO_STAGE 的处理程序中，您应该取消注册它。

【参考方案1】：

//使用弱引用，以便在必要时处理监听器

this.addEventListener(Event.ADDED_TO_STAGE, init, false, 0, true);

private function init(e:Event):void 

//remove this now as we have added the object to the stage
this.removeEventListener(Event.ADDED_TO_STAGE, init);

//add a new listener that will fire when the object is removed from stage
this.addEventListener(Event.REMOVED_FROM_STAGE, reset, false, 0, true);

...

private function reset(e:Event):void 

//this function is called when the object has been removed from the stage
this.removeEventListener(Event.REMOVED_FROM_STAGE, reset);

//now make sure all timers and stopped and nulled if required
//as well as all objects removed from stage and nulled if required. e.g.

fireTimer.stop();
fireTimer = null;

enemyArray = [];
enemyArray = null;

enemy

removeChild(Background);
Background = null;

removeChild(avatar);
avatar = null;

gameTimer.stop();
gameTimer = null;

_collisionTest = null;

//注意。您正在向舞台添加星星，但无法通过引用它们来移除它们。

for (var i:int = 0; i < numStars; i++)

   stage.addChildAt(new Star(stage), 1);

//您可能希望将它们添加到数组中，以便删除它们。

var starArray = [];

for (var i:int = 0; i < numStars; i++)

   var newStar:Star = new Star(stage);
   stage.addChildAt(newStar, 1);
   starArray.push(newStar);

然后删除它们：

for (var i:int = starArray.length; i > 0; i--)


   stage.removeChild(starArray[starArray.length-1]);


starArray = [];
starArray = null;

【讨论】：

错误：错误 #2094：事件调度递归溢出。在 flash.display::DisplayObjectContainer/removeChild() 在 States/changeState() 在 AvoiderGame/reset() 在 flash.display::DisplayObjectContainer/removeChild() 在 States/changeState() 在 AvoiderGame/onTick() 在 flash.utils ::Timer/_timerDispatch() at flash.utils::Timer/tick() 这是自从我添加重置功能以来我一直得到的。

作为一般调试过程的一部分，如果错误不是很明显，请尝试将所有内容注释掉，然后取消注释并测试每一行代码块以查看错误何时出现。关于您的错误，请在执行任何其他操作之前尝试停止两个计时器。