Actionscript 3.0, error with hitTestObject

Question

I'm getting an error I can't seem to fix. I think I know kind of what is going on but I'm not sure enough to be able to fix it. I keep getting error

"TypeError: Error #2007: Parameter hitTestObject must be non-null.

at flash.display::DisplayObject/_hitTest()

at flash.display::DisplayObject/hitTestObject()"

Basically I fire an attack in my game. It hits an enemy and he is killed just fine. BUT, he has an animation as he dies that takes a couple seconds. It seems if I fire another attack during his animation, my attack IMMEDIATELY gives this error (before striking anything, that is). Once the animation is over, everything is fine again. Also, the game was working 100% fine before I put in this animation.

Here is my document class

package com.classes 
{
    import flash.display.MovieClip;
    import flash.display.Stage;
    import flash.events.Event;

    public class DocumentClass extends MovieClip
    {

        // we need to keep track of our enemies.
        public static var enemyList1:Array = new Array();
        // moved stickobject1 to a class variable.
        private var stickobject1:Stickman2;

        public function DocumentClass() : void
        {
            //removed the var stickobject1:Stickman2 because we declared it above.
            var bg1:background1 = new background1();
            stage.addChild(bg1);

            stickobject1 = new Stickman2(stage);
            stage.addChild(stickobject1);

            stickobject1.x=50;
            stickobject1.y=300;

            //running a loop now.... so we can keep creating enemies randomly.
            addEventListener(Event.ENTER_FRAME, loop, false, 0, true);

        }

        //our loop function
        private function loop(e:Event) : void
        {
            //run if condition is met.
            if (Math.floor(Math.random() * 90) == 5)
            {
                //create our enemyObj1 
                var enemyObj1:Enemy1 = new Enemy1(stage, stickobject1);

                //listen for enemyObj1 being removed from stage
                enemyObj1.addEventListener(Event.REMOVED_FROM_STAGE, removeEnemyObj1, false, 0, true);

                //add our enemyObj1 to the enemyList1
                enemyList1.push(enemyObj1);

                stage.addChild(enemyObj1);
            }   
        }

        private function removeEnemyObj1(e:Event)
        {
            enemyList1.splice(enemyList1.indexOf(e.currentTarget), 1);
        }


    }

}

And here is my attack1 class

package com.classes {

    import flash.display.MovieClip;
    import flash.display.Stage;
    import com.senocular.utils.KeyObject;
    import flash.ui.Keyboard;
    import flash.events.Event;


    public class attack1 extends MovieClip {


        private var stageRef:Stage;
        private var bulletSpeed:Number = 16;

        public function attack1 (stageRef:Stage, x:Number, y:Number) : void
        {
            this.stageRef = stageRef;
            this.x = x;
            this.y = y;

            addEventListener(Event.ENTER_FRAME, loop, false, 0, true);
        }

        private function loop(e:Event) : void
        {
            //move bullet up
            x += bulletSpeed;

            if (x > stageRef.stageWidth) 
                removeSelf();

            for (var i:int = 0; i < DocumentClass.enemyList1.length; i++)
            {
                if (hitTestObject(DocumentClass.enemyList1[i].hit))
                {
                    trace("hitEnemy");
                    removeSelf();
                    DocumentClass.enemyList1[i].takeHit();
                }
            }
        }

        private function removeSelf() : void
        {
            removeEventListener(Event.ENTER_FRAME, loop);

            if (stageRef.contains(this))
                    stageRef.removeChild(this);
        }

    }

}

Don't think you should need any other of my classes to figure out what's going on, but let me know if you do! Thanks very much =)

Answer 1

Not the correct solution in this question. You can always do != null in a conditional statement.

if(object!=null){
    party.drink();
}

Answer 2

You don't want to do a hit test against any object that may have been removed from the scene (or from the enemyList array). The extra condition added to attack1.loop's for loop should get rid of your error. A better fix is to splice out the items you remove, so they are never tested against in the loop.

The break line will make it stop trying to hit other enemies after the bullet is removed. If the line "DocumentClass.enemyList1[i].takeHit();" removes the item from the enemyList1, you need to make sure you use "i--;" at the bottom of the loop as well, if you plan on looping through the remainder of the enemies. "i--" or "break", you will probably need one of them in that loop.

Double check the order in which you are executing your removal methods. Sometimes it's better to flag the items for removal and remove them in a separate loop than to remove an item that may be needed later in the same loop.

for (var i:int = 0; i < DocumentClass.enemyList1.length; i++){
  if(DocumentClass.enemyList1[i] && DocumentClass.enemyList1[i].hit){
    if (hitTestObject(DocumentClass.enemyList1[i].hit)){
      trace("hitEnemy");
      removeSelf();
      DocumentClass.enemyList1[i].takeHit();
      break;
    }
  }
}