Question

好的，所以当我的激光击中敌人时，我想要移除激光和敌人我的循环以某种方式在索引之外搜索并使程序崩溃。我做错了什么？

package 
{
    import flash.display.Sprite;
    import flash.events.Event;
    import flash.events.MouseEvent;
    import flash.events.TimerEvent;
    import flash.geom.Rectangle;
    import flash.ui.Mouse;
    import flash.utils.Timer;

    [SWF(width = 500, height = 500, frameRate = 25, backgroundColor = 0x000000)]

    public class Main extends Sprite 
    {
        private var craft:Craft = new Craft();
        private var laser:Laser;
        private var laserCollection:Vector.<Laser> = new Vector.<Laser>;
        private var laserSpeed:Number = 5;

        private var newEnemyTimer:Timer = new Timer(2000);
        private var enemy:Enemy;
        private var enemyCollection:Vector.<Enemy> = new Vector.<Enemy>;
        private var enemySpeed:Number = 5;

        public function Main()
        {
            addChild(craft);
            //Create a bounding box for the draggable area.
            var rect:Rectangle = new Rectangle(12, 460, 476, 0);
            //If you set startDrags first parameter, LockCenter to true, you don't have to explicitly set the targets position to the mouses position.
            craft.startDrag(true, rect);
            Mouse.hide();

            newEnemyTimer.start();
            newEnemyTimer.addEventListener(TimerEvent.TIMER, newEnemy);

            stage.addEventListener(MouseEvent.CLICK, shoot);

            addEventListener(Event.ENTER_FRAME, update);
        }   

        private function update(e:Event):void
        {
            updateLasers();
            updateEnemies();
            checkForHit();

            trace("lasers:" + laserCollection.length + ", enemies:" + enemyCollection.length);
        }

        private function checkForHit():void
        {
            if (laserCollection.length > 0)
            {
                for (var i:int = 0; i < laserCollection.length; i++) 
                {
                    for (var j:int = 0; j < enemyCollection.length; j++) 
                    {
                        if (laserCollection[i].hitTestObject(enemyCollection[j]))
                        {
                            removeChild(laserCollection[i]);
                            laserCollection.splice(i, 1);

                            removeChild(enemyCollection[j]);
                            enemyCollection.splice(j, 1);

                            //The program crashes here because the index is outside the reach,
                            //i.e if I have 8 laser beams out and only 3 enemies, it tries to remove enemy[8]
                            // I THINK???
                        }
                    }
                }
            }
        }

        private function updateLasers():void
        {
            if (laserCollection.length > 0)
            {
                for (var i:int = 0; i < laserCollection.length; i++) 
                {
                    if (laserCollection[i].y > 10)
                    {
                        laserCollection[i].y -= laserSpeed;
                        laserCollection[i].alpha -= 0.01;
                    }
                    else
                    {
                        //Can the problem be that I also remove the laser here?
                        //It seem to crash even if I hit an enemy at the bottom of the stage so shouldn't be.
                     removeChild(laserCollection[i]);
                     laserCollection.splice(i, 1);
                    }
                }
            }
        }

        private function updateEnemies():void
        {
            if (enemyCollection.length > 0)
            {
                for (var i:int = 0; i < enemyCollection.length; i++) 
                {
                    if (enemyCollection[i].y < 500)
                    {
                        enemyCollection[i].y += enemyCollection[i].getSpeed();
                    }
                    else
                    {
                        enemyCollection[i].y = -20;
                        enemyCollection[i].setSpeed();
                        enemyCollection[i].x = Math.random() * stage.stageWidth;
                    }
                }
            }
        }

        private function newEnemy(e:TimerEvent):void
        {
            enemy = new Enemy();
            addChild(enemy);
            enemy.x = Math.random() * stage.stageWidth;
            enemy.y = -30;
            enemyCollection.push(enemy);
        }

        private function shoot(e:MouseEvent):void
        {
            laser = new Laser();
            addChild(laser);
            laserCollection.push(laser);
            laser.x = craft.x;
            laser.y = craft.y;
        }
    }   
}

Answer 1

在迭代时删除数组元素会导致问题：当您在array[i]处删除元素时，以下元素将向上移动。在删除元素后，您在同一周期中仍然有array[i]的元素。当下一个循环周期开始时，i会递增 - 所以你只是跳过了一个元素。

两种可能的解决方案：

如果您删除了元素，则减少计数器（在您的情况下为i和j）。
向后循环，因此尚未检查的元素的索引不会改变。

另一件事：此处不需要if (laserCollection.length > 0)等检查，因为如果集合为空，循环将无法运行。

想要在我们点击它们时移除孩子，但索引似乎已关闭

1 个答案: