# Mix between external classes and timeline ActionScript

**URL:** <https://forum.kirupa.com/t/mix-between-external-classes-and-timeline-actionscript/282859>\
**Category:** flash\
**Created:** [February 27, 2009, 7:30am UTC](https://forum.kirupa.com/t/mix-between-external-classes-and-timeline-actionscript/282859 "2009-02-27T07:30:23Z")\
**Posts on this page:** 1\
**Page:** 1

<div class="post-metadata">

**Author:** ![Beebs](https://avatars.discourse-cdn.com/v4/letter/b/47e85d/32.png) [@Beebs](https://forum.kirupa.com/u/Beebs)\
**Post date:** [February 27, 2009, 7:30am UTC](https://forum.kirupa.com/t/mix-between-external-classes-and-timeline-actionscript/282859/1 "2009-02-27T07:30:23Z")

</div>

I have external document class to instantiate movieclip to the stage which is contained scrollbar. Within this movieclip there’s scrollbar AS ( from Lee Brimelow ) as follows :

```auto

import caurina.transitions.*;

var yOffset:Number;
var yMin:Number = 0;
var yMax:Number;

function ScrollBar():void
		{
			sb.thumb.buttonMode = true;
			yMin = 0;
			yMax = sb.track.height - sb.thumb.height;
			sb.thumb.addEventListener(MouseEvent.MOUSE_DOWN, thumbDown);
			stage.addEventListener(MouseEvent.MOUSE_UP, thumbUp);
			
		}

function thumbDown(e:MouseEvent):void
{
	stage.addEventListener(MouseEvent.MOUSE_MOVE, thumbMove);
	yOffset = mouseY - sb.thumb.y;
}

function thumbUp(e:MouseEvent):void
{
	stage.removeEventListener(MouseEvent.MOUSE_MOVE, thumbMove);
}

function thumbMove(e:MouseEvent):void
{
	sb.thumb.y = mouseY - yOffset;
	if(sb.thumb.y <= yMin)
		sb.thumb.y = yMin;
	if(sb.thumb.y >= yMax)
		sb.thumb.y = yMax;
	var sp:Number = sb.thumb.y / yMax;
	Tweener.addTween(body_txt, {y:(-sp*(body_txt.height-masker.height)), time:1});
	e.updateAfterEvent();
}

ScrollBar();

```

Somehow I got this error message

```auto

TypeError: Error #1009: Cannot access a property or method of a null object reference.
	at Body_mc/ScrollBar()
	at Body_mc/frame1()

```

Can someone show me where did I go wrong?  
Thanks a lot