ItemRenderer fails updating values with a sort applied to the ArrayCollection (dataProvider)

Question

Hello everyone,
Im updating the ArrayCollection that is the source of my list component
(the email never changes)
o:Object = {user:"username",email:"emailAdress",state:"number",imageURL="urlToImage"} //This comes from a function and arrives well.
for (var j:int = 0; j < _arcUserList.length; j++)
          if(_arcUserList.getItemAt(j).email == o.email)
                //_arcUserList.setItemAt(o,j) //I've tried this but doesn't work too!!
              _arcUserList.getItemAt(j).user = o.user;
              _arcUserList.getItemAt(j).email = o.email;
              _arcUserList.getItemAt(j).state = o.state;
              _arcUserList.getItemAt(j).imageURL = o.imageURL;
              _arcUserList.itemUpdated(_arcUserList.getItemAt(j));
This works well without the next sort settings, but if i add this lines in the init() it gives me:
Error #1009: Cannot access a property or method of a null object reference (in the first line of the onChange function of Renderer in red below)
var iSortByState:ISortField = new SortField("state",true);
var iSortByName:ISortField = new SortField("user",false);
var sort:Sort = new Sort();
sort.fields = [iSortByState,iSortByName];
_arcUserList.sort = sort;
_arcUserList.refresh();
here i post my item renderer
<?xml version="1.0" encoding="utf-8"?>
<s:ItemRenderer xmlns:fx="http://ns.adobe.com/mxml/2009"
                                        xmlns:s="library://ns.adobe.com/flex/spark"
                                        xmlns:mx="library://ns.adobe.com/flex/mx"
                                        width="100%"
                                        autoDrawBackground="true"
                                        creationComplete="fncInit(event)"
                                        dataChange="onChange(event)">
          <s:layout>
                    <s:HorizontalLayout gap="10" horizontalAlign="left"
                                                                      paddingTop="5" paddingBottom="5"
                                                                      paddingLeft="10" paddingRight="10"
                                                                      verticalAlign="middle"/>
          </s:layout>
          <s:Image id="_imgUser" height="32" width="32" />
          <s:VGroup width="70%">
                    <s:Label id="_lblUsername" fontSize="12" fontWeight="bold" />
                    <s:Label id="_lblState" color="#868686" fontSize="10" fontStyle="italic" />
          </s:VGroup>
          <s:HGroup width="100%"  horizontalAlign="right">
                    <s:Button width="40" label="@" click="onClickButton(event)" visible="false"/>
          </s:HGroup>
          <fx:Script>
                    <![CDATA[
                              import flash.filters.*;
                              import mx.collections.ArrayList;
                              import mx.controls.Alert;
                              import mx.events.FlexEvent;
                              import mx.events.StateChangeEvent;
                              [Bindable]private var arrStates:Array =["Disconnected","Busy","Available"];
                              [Bindable]private var _nState:Number;
                              [Bindable]private var _sImgURL:String;
                              [Bindable]private var _sUser:String;
                              [Bindable]private var _sEmail:String;
                              protected function fncInit(event:FlexEvent):void
                                        _nState = this.data.state;
                                        _sImgURL = this.data.imageURL;
                                        _sUser = this.data.user;
                                        _sEmail = this.data.email;
                                        this.setStyle("contentBackgroundColor","0xFF0000");
                                        _imgUser.smooth = true;
                                        fncLoadPicture(_sImgURL);
                                        _lblUsername.text = this.data.user;
                                        _lblState.text = arrStates[this.data.state];
                              private function fncLoadPicture(sURL:String):void{
                                        var context:LoaderContext = new LoaderContext();
                                        context.checkPolicyFile = true;
                                        context.applicationDomain = ApplicationDomain.currentDomain;
                                        var fotoLoader:Loader = new Loader();
                                        fotoLoader.contentLoaderInfo.addEventListener(Event.COMPLETE, onImageLoaded);
                                        fotoLoader.contentLoaderInfo.addEventListener(IOErrorEvent.IO_ERROR, onImageError);
                                        fotoLoader.load(new URLRequest(sURL), context);
                              private function onImageLoaded(event:Event):void {
                                        var bmp:Bitmap;
                                        bmp = ( event.target as LoaderInfo ).content as Bitmap;
                                        _imgUser.source = bmp;
                              private function onImageError(event:Event):void {
                                        Alert.show("Error loading imabe.", "Alert");
                              protected function onClickButton(event:MouseEvent):void
                                        trace(data.user+": "+data.state);
                              protected function onChange(event:FlexEvent):void
                                        _lblUsername.text = this.data.user; //if i comment this, it fails in the next and so on.
                                        _lblState.text = arrStates[this.data.state];
                                        fncLoadPicture(this.data.imageURL);
                                        var glow:GlowFilter = new GlowFilter();
                                        glow.alpha=0.8;
                                        glow.blurX=2;
                                        glow.blurY=2;
                                        glow.strength=30;
                                        glow.inner=false;
                                        glow.quality=BitmapFilterQuality.HIGH;
                                        switch (this.data.state.toString())
                                                  //Disconnected - Invisible
                                                  case "0":
                                                            _lblUsername.setStyle("color",0x555555);
                                                            glow.color=0x6E6E6E;
                                                            var matrix:Array = new Array();
                                                            matrix=matrix.concat([0.4,0.4,0.4,0,0]);// red
                                                            matrix=matrix.concat([0.4,0.4,0.4,0,0]);// green
                                                            matrix=matrix.concat([0.4,0.4,0.4,0,0]);// blue
                                                            matrix=matrix.concat([0,0,0,0.5,0]);// alpha
                                                            var cmf:ColorMatrixFilter=new ColorMatrixFilter(matrix);
                                                            _imgUser.filters=[cmf,glow];
                                                  break;
                                                  //Busy
                                                  case "1":
                                                            glow.color=0xDF0101;
                                                            _imgUser.filters=[glow];
                                                            break;
                                                  //Available
                                                  case "2":
                                                            glow.color=0x01DF01;
                                                            _imgUser.filters=[glow];
                                                            break;
                    ]]>
          </fx:Script>
</s:ItemRenderer>
It Works well until i put the sort.
Any suggestion?

Answer 1

TypeError: Error #1009: Cannot access a property or method of a null object reference.
          at usersRenderer/onChange()[D:\Mis Documentos\Proyectos\ACplugin\PorHerramientas\Flex\ac_videocall\src\usersRenderer.mxml:98 ]
          at usersRenderer/___usersRenderer_ItemRenderer1_dataChange()[D:\Mis Documentos\Proyectos\ACplugin\PorHerramientas\Flex\ac_videocall\src\usersRenderer.mxml:8]
          at flash.events::EventDispatcher/dispatchEventFunction()
          at flash.events::EventDispatcher/dispatchEvent()
          at mx.core::UIComponent/dispatchEvent()[E:\dev\4.y\frameworks\projects\framework\src\mx\core \UIComponent.as:13152]
          at spark.components::DataRenderer/set data()[E:\dev\4.y\frameworks\projects\spark\src\spark\components\DataRenderer.as:123]
          at spark.components::DataGroup/http://www.adobe.com/2006/flex/mx/internal::itemRemoved()[E:\dev\4.y\frameworks\projects\spark\src\spark\components\DataGroup.as:1761]
          at spark.components::DataGroup/adjustAfterMove()[E:\dev\4.y\frameworks\projects\spark\src\sp ark\components\DataGroup.as:1941]
          at spark.components::DataGroup/http://www.adobe.com/2006/flex/mx/internal::dataProvider_collectionChangeHandler()[E:\dev\4.y\frameworks\projects\spark\src\spark\components\DataGroup.as:1858]
          at flash.events::EventDispatcher/dispatchEventFunction()
          at flash.events::EventDispatcher/dispatchEvent()
          at mx.collections::ListCollectionView/dispatchEvent()[E:\dev\4.y\frameworks\projects\framewo rk\src\mx\collections\ListCollectionView.as:1024]
          at mx.collections::ListCollectionView/moveItemInView()[E:\dev\4.y\frameworks\projects\framew ork\src\mx\collections\ListCollectionView.as:1629]
          at mx.collections::ListCollectionView/handlePropertyChangeEvents()[E:\dev\4.y\frameworks\pro jects\framework\src\mx\collections\ListCollectionView.as:1421]
          at mx.collections::ListCollectionView/listChangeHandler()[E:\dev\4.y\frameworks\projects\fra mework\src\mx\collections\ListCollectionView.as:1316]
          at flash.events::EventDispatcher/dispatchEventFunction()