Question

This looks long but it’s a really simple question. With the following code:

public class Map extends MovieClip
{

    var dragdrops:Array;
    var numOfMatches:uint = 0;
    var speed:Number = 25;

    public function Map()
    {
        // constructor code
        var dragdrops = [one_mc,two_mc,three_mc,four_mc,five_mc,six_mc];

        var currentObject:DragDrop;

        for (var i:uint = 0; i < dragdrops.length; i++)
        {
            currentObject = dragdrops[i];
            currentObject.target = getChildByName(currentObject.name + "_target");
        }


    }

    public function match():void
    {
        numOfMatches++;
        if(numOfMatches == dragdrops.length)
        {
            win.addEventListener(Event.ENTER_FRAME, winGame);
        }
    }

I get this error

TypeError: Error #1009: Cannot access a property or method of a null
object reference. at Map/match()[G:_flash\edu\drag_drop\Map.as:34]
at DragDrop/drop()[G:_flash\edu\drag_drop\DragDrop.as:41]

I assume it’s because i’m referencing the global array “dragdrops” which currently is a null value.

However the code below works perfectly, by passing the dragdrops.length value to another global variable.

public class Map extends MovieClip
{

    var dragdrops:Array;
    var dragdropslength:Number = 0;
    var numOfMatches:uint = 0;
    var speed:Number = 25;

    public function Map()
    {
        // constructor code
        var dragdrops = [one_mc,two_mc,three_mc,four_mc,five_mc,six_mc];

        var currentObject:DragDrop;

        for (var i:uint = 0; i < dragdrops.length; i++)
        {
            currentObject = dragdrops[i];
            currentObject.target = getChildByName(currentObject.name + "_target");
        }

        dragdropslength = dragdrops.length

    }

    public function match():void
    {
        numOfMatches++;
        if(numOfMatches == dragdropslength)
        {
            win.addEventListener(Event.ENTER_FRAME, winGame);
        }
    }

While this works fine I was wondering if there was a more elegant solution to be able to reference the dragdrops value from within the Map() constructor without the extra variable.

Answer 1

You can assign to “dragdrops” directly in the constructor, thereby initializing the instance variable. Just remove the preceding “var” in the first line of the Map constructor.