substring from an array as3 **Error #1009: Cannot access a property or method of a null object reference

Question

I am trying to create a matching game where one object in the array hitBoxes is matched to one object in the array hitBoxes2. I have tried to convert the instance name into a string and then used the substring method to match the LAST number in the instance name, if its a match they win. Right now I'm getting the error

TypeError: Error #1009: Cannot access a property or method of a null object reference. at MethodInfo-499()

I'm wondering if anyone can help me. Thanks!

            var left:String;
            var correct:MovieClip = new Correct;
            var isClicked:Boolean = false;
            var leftClicked:int = 0;

            p3.nextPage.buttonMode = true;
            p3.nextPage.addEventListener(MouseEvent.CLICK, nextPage);

            function nextPage(MouseEvent):void{
                removeChild(p3);
            }

            var hitBoxes:Array = [p3.a1, p3.a2, p3.a3, p3.a4, p3.a5, p3.a6, p3.a7, p3.a8];
            var hitBoxes2:Array = [p3.b1, p3.b2, p3.b3, p3.b4, p3.b5, p3.b6, p3.b7, p3.b8];


            for (var h:int = 0; h < hitBoxes.length; h++){
                hitBoxes[h].buttonMode = true;
                hitBoxes[h].addEventListener(MouseEvent.CLICK, matchingLeft);
            }

            for (var h2:int = 0; h2 < hitBoxes2.length; h2++){
                hitBoxes2[h2].buttonMode = true;
                hitBoxes2[h2].addEventListener(MouseEvent.CLICK, matchingRight);
            }

            function matchingLeft(e:MouseEvent):void{
                var left = String(e.currentTarget.name);
                isClicked = true;
                trace(left);
            }

            function matchingRight(e:MouseEvent):void{
                var right:String = String(e.currentTarget.name);
                trace(right);
                if(isClicked == true && left.substring(3,3) == right.substring(3,3)){
                    trace("matched");
                }

            }

DigitalD · Accepted Answer · 2012-12-05 20:42:07Z

2

According to your code variable "left" is null at matchingRight method, because matchingLeft uses its local variable with name "left", and top-level "left" still has its default value.

also String.substring method is used incorrectly:

var name:String="p3.a1";
trace(name.substring(3, 3)); // this will always output empty string ""
trace(name.substring(4, 5)); // this will output "1" string

in conclusion I'd advise to use array indices (integers) instead of strings when calculating "matched" condition, substring operation and string comparison are CPU intensive.

edited Dec 5, 2012 at 20:42

answered Dec 5, 2012 at 19:48

DigitalD

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