Reputation: 912

ScrollPane set scroll position

I can not control the scrolling of a scrollpane from within my actionscript (I am using actionscript 3.0)

Here is my Definition:

var scrollPane:ScrollPane = new ScrollPane();
scrollPane.verticalScrollPolicy = "false";
scrollPane.move(374, 0);
scrollPane.setSize(476, 370);

When I try to set it - scrollPane.horizontalScrollPosition = 500; I get the following error

TypeError: Error #1009: Cannot access a property or method of a null object reference.
    at fl.containers::ScrollPane/setScrollDrag()
    at fl.containers::ScrollPane/draw()
    at fl.core::UIComponent/drawNow()
    at fl.containers::BaseScrollPane/set horizontalScrollPosition()
    at Program()
    at Preloader/main()
    at Preloader/enterFrameHandler()

Even scrollPane.horizontalScrollPosition = scrollPane.horizontalScrollPosition; throws the same error.

However trace(scrollPane.horizontalScrollPosition); works just fine.

I have tried hPosition also and it does not work at all. Any clues as to how I can control the scroll position would be greatly appreciated.

Below is the entire code

package {
    import flash.display.*;
    import flash.events.*;
    import flash.filters.*;
    import fl.transitions.Tween;
    import fl.transitions.easing.*;
    import fl.containers.ScrollPane;


    public class Program extends Sprite {
        public function Program() {
            //define variable
            var startX:Number;
            var startY:Number;
            var counter:Number = 0;
            const LIMIT:Number = 100;
            var intMessages:Number = 80;
            var intBoardSize:Number = 476*(Math.round(intMessages/15)+1);
            var intMessageMinX:Number = 35;
            var intMessageMaxX:Number = intBoardSize-99;
            var intMessageMinY:Number = 35;
            var intMessageMaxY:Number = 310;
            var activeGloveName:String = ""
            var intDegreeHigh:Number = 45;
            var intDegreeLow:Number = -45;

            //create objects
            var mcglove:mcGlove = new mcGlove();
            var mcglovetarget:mcGloveTarget = new mcGloveTarget();
            var myDropShadowFilterSmall = new DropShadowFilter (2,45,0x000000,0.65,3,3,2,3,false,false,false);
            var myDropShadowFilterDown = new DropShadowFilter (3,45,0x000000,0.65,5,5,2,3,false,false,false);
            var myDropShadowFilterUp = new DropShadowFilter (5,45,0x000000,0.65,7,7,2,3,false,false,false);
            var topShadow = new DropShadowFilter (3,90,0x000000,0.35,8,8,2,3,false,false,false);
            var holder:MovieClip = new MovieClip();
            var pinkline:Sprite = new Sprite();
            var searchBox:Sprite = new Sprite();
            var topShadowBox:Sprite = new Sprite();
            var aMessages:Array = new Array();


            //Create a glove for each message
            for (var x = 0; x < intMessages; x++){
                aMessages[x] = new mcGlove();
                aMessages[x].scaleX = .28;
                aMessages[x].scaleY = .28;
                counter = 0;
                position(aMessages[x]);
                aMessages[x].rotation = (0, 0, 0, Math.round(Math.random() * (intDegreeHigh - intDegreeLow)) + intDegreeLow);
                aMessages[x].filters = [myDropShadowFilterSmall];
                holder.addChild(aMessages[x]);
                aMessages[x].name = "glove" + x;
                aMessages[x].addEventListener(MouseEvent.MOUSE_DOWN, selectMessage);
                aMessages[x].addEventListener(MouseEvent.MOUSE_UP, releaseMessage);
                aMessages[x].buttonMode = true;
            }

            var scrollPane:ScrollPane = new ScrollPane();
            scrollPane.verticalScrollPolicy = "false";
            scrollPane.move(374, 0);
            scrollPane.setSize(476, 370);
            scrollPane.horizontalLineScrollSize = 120;


            topShadowBox.graphics.beginFill(0x333333);
            topShadowBox.graphics.drawRect(0,0,870,5);
            topShadowBox.x = -10;
            topShadowBox.y = -5;
            topShadowBox.filters = [topShadow];

            pinkline.graphics.beginFill(0xDB9195);
            pinkline.graphics.drawRect(0,0,476,2);
            pinkline.x = 374;
            pinkline.y = 353;

            searchBox.graphics.beginFill(0xDB9195);
            searchBox.graphics.drawRect(0,0,476,25);
            searchBox.x = 374;
            searchBox.y = 370;

            //add to frame
            sortObjects();

            scrollPane.source = holder;

            scrollPane.horizontalScrollPosition = 5;

            //create instance names for referancing/compairing objects
            mcglove.name = "mcglove";
            mcglovetarget.name = "mcglovetarget";

            //position the glove and modify apperiance
            mcglove.x = 163;
            mcglove.y = 211;
            mcglove.filters = [myDropShadowFilterDown];
            mcglovetarget.x = 615;
            mcglovetarget.y = 211;
            mcglovetarget.alpha = 0

            //action listeners
            mcglove.addEventListener(MouseEvent.MOUSE_DOWN, selectGlove);
            mcglove.addEventListener(MouseEvent.MOUSE_UP, releaseGlove);

            function position(target) {
                target.x = Math.round(Math.random() * (intMessageMaxX - intMessageMinX)) + intMessageMinX;
                target.y = Math.round(Math.random() * (intMessageMaxY - intMessageMinY)) + intMessageMinY;
                for (var i:uint=0; i<aMessages.length -1 ; i++) {
                    if(target.hitTestObject(aMessages[i]) && counter < LIMIT){
                        counter++;
                        position(target);
                        return false;
                    };
                }
            } 

            function selectGlove(event:MouseEvent):void {
                event.target.startDrag(true);
                var myTargetName:String = event.target.name + "target";
                var myTarget:DisplayObject = getChildByName(myTargetName);
                mcglove.filters = [myDropShadowFilterUp];
                addChild(myTarget);
                event.target.parent.addChild(event.target);
                addChild(topShadowBox);
                myTarget.alpha = .5;
                startX = event.target.x;
                startY = event.target.y;
            }

            function releaseGlove(event:MouseEvent):void {
                event.target.stopDrag();
                var myTargetName:String = event.target.name + "target";
                var myTarget:DisplayObject = getChildByName(myTargetName);
                event.target.filters = [myDropShadowFilterDown];
                myTarget.alpha = 0;

                if (event.target.dropTarget != null && event.target.dropTarget.parent == myTarget){
                    event.target.removeEventListener(MouseEvent.MOUSE_DOWN, selectGlove);
                    event.target.removeEventListener(MouseEvent.MOUSE_UP, releaseGlove);
                    event.target.x = myTarget.x;
                    event.target.y = myTarget.y;
                    var myTween:Tween = new Tween(getChildByName(event.target.name), "scaleX",Strong.easeOut,getChildByName(event.target.name).scaleX,.28,2,true);
                    var myTween2:Tween = new Tween(getChildByName(event.target.name), "scaleY",Strong.easeOut,getChildByName(event.target.name).scaleY,.28,2,true);
                    holder.addChild(getChildByName(event.target.name));
                    scrollPane.source = holder;
                    holder.getChildByName(event.target.name).x=Math.round(Math.random() * (470+Math.round(scrollPane.horizontalScrollPosition) - Math.round(scrollPane.horizontalScrollPosition))) + Math.round(scrollPane.horizontalScrollPosition);
                    holder.getChildByName(event.target.name).y=Math.round(Math.random() * (intMessageMaxY - intMessageMinY)) + intMessageMinY;
                    holder.getChildByName(event.target.name).addEventListener(MouseEvent.MOUSE_DOWN, selectMessage);
                    holder.getChildByName(event.target.name).addEventListener(MouseEvent.MOUSE_UP, releaseMessage);
                } else {
                    event.target.x = startX;
                    event.target.y = startY;
                }

                //sortObjects();
                addChild(scrollPane);
                addChild(pinkline);
                addChild(topShadowBox);
            }

            function selectMessage(event:MouseEvent):void{
                if (activeGloveName != ""){
                    var activeGlove:DisplayObject = holder.getChildByName(activeGloveName);
                    activeGlove.filters = [myDropShadowFilterSmall];
                    activeGlove.scaleX = .28;
                    activeGlove.scaleY = .28;


                holder.addChild(activeGlove);
                }
                activeGloveName = event.target.name;
                //event.target.dragIt();
                holder.addChild(holder.getChildByName(event.target.name));
                event.target.filters = [new GlowFilter(0xABEEFC, .65, 15, 15, 1, 1, false, false)];
                event.target.scaleX = .35;
                event.target.scaleY = .35;
            }

            function releaseMessage(event:MouseEvent):void{
                event.target.dropIt();
            }

            function sortObjects():void{
                addChild(mcglovetarget);
                addChild(scrollPane);
                addChild(pinkline);
                addChild(searchBox);
                addChild(mcglove);
                addChild(topShadowBox);
            }

            mcglove.buttonMode = true;

        }
    }
}

Upvotes: 0

Answers (4)

Roman

Reputation: 1

You should add ScrollPane to stage firstly. If scrollPane.stage == null you will have such error.

Upvotes: 0

SuperIRis

Reputation: 413

I had the same problem and figured out what caused it. At least in my case, the problem was that the scrollpane was not yet a child of stage.

This causes the error you describe:

sp.verticalScrollPosition = 0;    
this.addChild(sp)

While this works fine:

this.addChild(sp)
sp.verticalScrollPosition = 0;

Hope it helps :)

Upvotes: 3

ForYourOwnGood

Reputation: 40442

If you look at the error trace, the error is occuring inside of

fl.containers::ScrollPane/setScrollDrag().

If you look here you find out that scrollDrag ...

Gets or sets a value that indicates whether scrolling occurs when a user drags on content within the scroll pane.

You never put content into the scroll pane

scrollPane.source = "...";

I believe this is why the error is occuring, try putting some content into the scrollpane before you set the horizontalScrollPosition.

Upvotes: 1

James Hay

Reputation: 12720

horizontalScrollPosition is a property of ScrollPane so you would set it through

scrollPane.horizontalScrollPosition = 500;

instead of a method call.

Upvotes: 1

ScrollPane set scroll position

Answers (4)

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