Issue : drag and drop from list control to tree control

Question

Hi,
I was trying a drag and drop from list control to tree control. I have used some sample data to populate list and tree controls .
It is working fine . except one problem ..
Prob : when i drag an item to tree control .. it gets added .. now tree contains (X+1) data in list .. say X is the inital number of nodes in a tree node.
          now if i drag another item from list to last item in the tree node  .. i.e at X+1 index. .. it throws null pointer exception.
I am considerably new in flex programming . looking for help from experts ..
Below is my code :
<?xml version="1.0" encoding="utf-8"?>
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml"
                layout="horizontal"
                creationComplete="init()">
    <mx:Script>
        <![CDATA[
            import mx.controls.listClasses.IListItemRenderer;
            import mx.rpc.events.FaultEvent;
            import mx.rpc.events.ResultEvent;
            import mx.utils.ObjectUtil;
            import mx.collections.ICollectionView;
            import mx.core.UIComponent;
            import mx.managers.DragManager;
            import mx.events.DragEvent;
            import mx.controls.Alert;
            import mx.controls.Label;
            import mx.events.CloseEvent;
            private var homePath:String="/home/e311394/dndTest/";
            private var destPath:String="/home/e311394/dndDest/";
            private var eid:String="e311394";
            private var actn:String;
            [Bindable]
            private var cm:ContextMenu;
            private var cmi:ContextMenuItem;
            [Bindable]
            private var dp:ArrayCollection;
            private function init():void
                cmi=new ContextMenuItem("Remove");
                cmi.enabled=true;
                cmi.addEventListener(ContextMenuEvent.MENU_ITEM_SELECT, contextMenuItem_menuItemSelect);
                cm=new ContextMenu();
                cm.hideBuiltInItems();
                cm.customItems=[cmi];
                cm.addEventListener(ContextMenuEvent.MENU_SELECT, contextMenuItem_menuSelect);
                list.contextMenu=cm;
            private function contextMenuItem_menuSelect(evt:ContextMenuEvent):void
                list.selectedIndex=lastRollOverIndex;
            private function contextMenuItem_menuItemSelect(evt:ContextMenuEvent):void
                var loclSelectedRow:Object=list.selectedItem;
                var lostrSelectedMenuItem:String;
                lostrSelectedMenuItem=evt.target.caption;
                if (loclSelectedRow != null)
                    var obj:Object=new Object()
                    obj.label=loclSelectedRow.label as String;
                        //Alert.show(obj.label);
                if (lostrSelectedMenuItem == "Remove")
                    if(loclSelectedRow!=null)
                    var pth:String=homePath.concat(loclSelectedRow.label);
                    //Alert.show(pth);
                    //FlexDnDRemoteService.process(eid,"delete",pth,"-"); 
                    var coll:ArrayCollection=list.dataProvider as ArrayCollection;
                    if (coll.contains(loclSelectedRow))
                        coll.removeItemAt(coll.getItemIndex(loclSelectedRow));
            public function onTreeDragEnter(event:DragEvent):void
                event.preventDefault();
                DragManager.acceptDragDrop(event.target as UIComponent);
                tree.showDropFeedback(event);
            protected function onTreeDragOver(event:DragEvent):void
                event.preventDefault();
                event.currentTarget.hideDropFeedback(event);
                try
                    var index:int=tree.calculateDropIndex(event);
                catch (e:Error)
                    DragManager.showFeedback(DragManager.NONE);
                    return;
                tree.selectedIndex=index;
                var draggedOverItem:Object=tree.selectedItem;
            public function onTreeDragExit(event:DragEvent):void
                event.preventDefault();
                tree.hideDropFeedback(event);
            private function showAlert():void
                Alert.yesLabel="Move";
                Alert.noLabel="Copy";
                Alert.buttonWidth=70;
                Alert.show("Copy / Move ?", "Confirm", Alert.YES | Alert.NO | Alert.CANCEL, this, alertListener, null, Alert.OK);
            private function alertListener(eventObj:CloseEvent):void
                var result:Boolean=false;
                if (eventObj.detail == Alert.CANCEL)
                    //Alert.show("CANCEL");
                    return;
                if (eventObj.detail == Alert.YES)
                    //Alert.show("YES");
                    result=true;
                else if (eventObj.detail == Alert.NO)
                    //Alert.show("NO");
                    result=false;
                var index:int=tree.calculateDropIndex(treedropevt);
                //Alert.show("Drop Pos" + index.toString());
                /* var treeList:ArrayCollection=tree.dataProvider as ArrayCollection;
                   Alert.show(" index"+index+"Length "+treeList.length);
                   if(index > treeList.length)
                   Alert.show("Returning");
                   return;
                var items:Array=new Array();
                if (treedropevt.dragSource.hasFormat("items"))
                    items=items.concat(treedropevt.dragSource.dataForFormat("items") as Array);
                var parentItem:Object;
                parentItem=getObjectTarget();
                /* if (tree.dataDescriptor.isBranch(tree.indexToItemRenderer(index).data))
                   parentItem=tree.indexToItemRenderer(index).data;
                   else
                   var dropParentPackage:Object = tree.mx_internal::_dropData.parent as Object;
                   Alert.show("HAck"+dropParentPackage.toString());
                   parentItem=tree.getParentItem(tree.indexToItemRenderer(index).data);
                   //Alert.show("Lenght "+ObjectUtil.getClassInfo(parentItem).properties.length);
                //Alert.show("Lenght "+ObjectUtil.getClassInfo(parentItem).properties.length);
                var position:int=0;
                /* if(ObjectUtil.getClassInfo(parentItem).properties.length==0)
                   Alert.show("Returning");
                   return;
                if (parentItem != null)
                    try
                        while (tree.indexToItemRenderer(index).data != parentItem)
                            //Alert.show(tree.indexToItemRenderer(index).data.toString());
                            if (index > 0)
                                index--;
                            //Alert.show("Insiade");
                            position++;
                    catch (e:Error)
                        Alert.show("Catch" + index.toString());
                        return;
                for each (var item:Object in items)
                    var obj:Object=new Object()
                    obj.label=item.label as String;
                    if (parentItem != null)
                        //Alert.show("ADDED");                       
                        tree.dataDescriptor.addChildAt(parentItem, obj, position++);                       
                    else
                        //Alert.show("PARENT NULL");
                        tree.dataDescriptor.addChildAt(tree.selectedItem, obj, position++);                       
                    var spth:String=homePath.concat(item.label);
                    //Alert.show(spth);   
                    var dpth:String=destPath.concat(item.label);
                    //Alert.show(dpth);
                    if (result == true)
                        removeItems();
                            //FlexDnDRemoteService.process(eid,"move",spth,dpth);
                    else
                        //FlexDnDRemoteService.process(eid,"copy",spth,dpth);
                    tree.validateNow();
            public function getObjectTarget():Object
                var dropData:Object=tree.mx_internal::_dropData as Object;
                if (dropData.parent != null)
                    return dropData.parent;
                else
                    // if there is not parent (root of the tree), I take the root directly
                    var renderer:IListItemRenderer=tree.indexToItemRenderer(0);
                    return renderer.data;
            public function removeItems():void
                //remove moved elements
                var items:Array=treedropevt.dragSource.dataForFormat("items") as Array;
                var coll:ArrayCollection=list.dataProvider as ArrayCollection;
                for each (var item:Object in items)
                    if (coll.contains(item))
                        coll.removeItemAt(coll.getItemIndex(item));
            private var treedropevt:DragEvent;
            public function onTreeDragDrop(event:DragEvent):void
                treedropevt=event;
                showAlert();
                event.preventDefault();
                tree.hideDropFeedback(event);
            public function resultHandler(event:ResultEvent):void
                Alert.show("Success", "Status");
            public function faultHandler(event:FaultEvent):void
                Alert.show(event.fault.faultString, "Failure");
        ]]>
    </mx:Script>
    <mx:ArrayCollection id="listDP">
        <mx:Object label="File1.dnd"/>
        <mx:Object label="File2.dnd"/>
        <mx:Object label="File3.dnd"/>
        <mx:Object label="File4.dnd"/>
        <mx:Object label="File5.dnd"/>
    </mx:ArrayCollection>
    <mx:Number id="lastRollOverIndex"/>
    <!--
         <mx:ArrayCollection id="treeDP">
         <mx:Object label="/home">
         <mx:children>
         <mx:Object label="dummy1.ks"/>
         <mx:Object label="dummy2.ks"/>
         <mx:Object label="e493126">
         <mx:children>
         <mx:ArrayCollection>
         <mx:Object label="/home/e493126/sample1.ks"/>
         </mx:ArrayCollection>
         </mx:children>
         </mx:Object>
         </mx:children>
         </mx:Object>
         </mx:ArrayCollection>
    -->
    <mx:ArrayCollection id="treeDP">
        <mx:Object label="/dndDest">
            <mx:children>
                <mx:ArrayCollection>
                    <mx:Object label="sample1.ks"/>
                    <mx:Object label="sample2.ks"/>
                    <mx:Object label="sample3.ks"/>
                    <mx:Object label="sample4.ks"/>
                    <mx:Object label="sample5.ks"/>
                    <mx:Object label="sample6.ks"/>
                </mx:ArrayCollection>
            </mx:children>
        </mx:Object>
    </mx:ArrayCollection>
    <mx:List id="list"
             itemRollOver="lastRollOverIndex = event.rowIndex"
             width="50%"
             dragEnabled="true"
             dataProvider="{listDP}"
             labelField="label"
             allowMultipleSelection="true"
             dragMoveEnabled="false">
    </mx:List>
    <mx:Tree id="tree"
             width="50%"            
             dragEnabled="true"            
             dataProvider="{treeDP}"            
             dragEnter="onTreeDragEnter(event)"
             dragOver="onTreeDragOver(event)"
             dragExit="onTreeDragExit(event)"
             dragDrop="onTreeDragDrop(event)"
             labelField="label"
             liveScrolling="true">
    </mx:Tree>
    <mx:RemoteObject id="FlexDnDRemoteService"
                     showBusyCursor="true"
                     destination="FlexDnD">
        <mx:method name="process"
                   result="resultHandler(event)"
                   fault="faultHandler(event)"/>
    </mx:RemoteObject>
</mx:Application>
Thanks,
Rajiv

Answer 1

Ya , i have searched and have used the same code.
But needed to customize few things like:
stop dnd in same tree
drop some item into a folder ..( onto it ) etc
have achieved the same .. but this issue ..
i think the tree dataprovider (contents internally is not being updated .. only the UI)
any suggestions ?
- Rajiv