Display List ItemRenderer Index in Flex3

Question

Is there a direct way to get the item index of the data inside an itemRenderer? I need to display the item number against each item. I am currently doing a workaround and won't allow reuse of my itemRenderer component.

var index:int = model.dataColl.getItemIndex(data) + 1;
itemNo = index.toString();

This is what i am using now, it works, but the concepts of component reuse and data abstraction are compromised.

I am using Flex 3.

score 2 · Accepted Answer · answered Aug 03 '11 at 07:02

The first answer seems to be working, but slow. It takes O(n^2) time as it runs through dataProvider array to get item index each time. We can access rowIndex from listData - it represents index of the current visible item. Vertical scroll position from parent List represents the amount of scrolled items:

<?xml version="1.0" encoding="utf-8"?>
<mx:HBox xmlns:mx="http://www.adobe.com/2006/mxml" implements="mx.controls.listClasses.IDropInListItemRenderer">
<mx:Script>
    <![CDATA[
        import mx.controls.listClasses.BaseListData;
        import mx.controls.listClasses.ListBase;

        [Bindable] private var index:int = 0;

        private var _listData:BaseListData;
        public function get listData():BaseListData
        {
            return _listData;
        }
        public function set listData(value:BaseListData):void
        {
            _listData = value;
        }

        override public function set data(value:Object):void
        {
            super.data = value;
            if (data && listData)
                index = _listData.rowIndex + ListBase(_listData.owner).verticalScrollPosition;
            else
                index = 0;
        }
    ]]>
</mx:Script>
<mx:Label text="{index}"/>
<mx:Label text="{data.toString()}"/>
</mx:HBox>

My list would display close to 1000 items, so I am using this in my project. Does the `verticalScrollPosition` indicate the number of items items that are out of view (above the visible List)? — midhunhk, Aug 03 '11 at 11:15
Actually `verticalScrollPosition` indicates the number of pixels that are out of the view, but with Lists (DataGrids and Trees) it indicates the number of such items. Try to increment or decrement it - the list will scroll by items, not by pixels. — moropus, Aug 03 '11 at 11:37
That's a cool observation, I had always thought things scroll in pixels, like Canvas and all. So its different for List based items, eh. I will keep in mind, this could come in handy :) — midhunhk, Aug 03 '11 at 12:25

score 1 · Answer 2 · answered Aug 02 '11 at 12:01

You can use labelFunction to solve your problem. For the simple test application:

<?xml version="1.0" encoding="utf-8"?>
<mx:Application creationComplete="init()" layout="absolute" xmlns:mx="http://www.adobe.com/2006/mxml">
    <mx:Script>
    <![CDATA[
        import mx.collections.ArrayCollection;

        private static const DATA_LENGTH:Number = 100;

        [Bindable]
        private var dp:ArrayCollection;

        private function countFinction(item:Object):String
        {
            return (dp.getItemIndex(item) + 1).toString();
        }

        private function init():void
        {
            var dataArray:Array = [];
            for (var i:int = 0; i < DATA_LENGTH; i++)
            {
                var item:Object = { firstName: "First" + (i + 1), lastName: "Last" + (i + 1) };
                dataArray.push(item);
            }
            dp = new ArrayCollection(dataArray);
        }
    ]]>
    </mx:Script>
    <mx:List dataProvider="{dp}" height="500" horizontalCenter="0" itemRenderer="TestRenderer"
        labelFunction="countFinction" verticalCenter="0" width="500" />
</mx:Application>

You can use the following test renderer:

<?xml version="1.0" encoding="utf-8"?>
<mx:HBox implements="mx.controls.listClasses.IDropInListItemRenderer" xmlns:mx="http://www.adobe.com/2006/mxml">
    <mx:Script>
    <![CDATA[
        import mx.controls.listClasses.BaseListData;

        private var _listData:BaseListData;

        /**
         * @inheritDoc
         */
        public function get listData():BaseListData
        {
            return _listData;
        }

        [Bindable(event = "listDataChanged")]
        /**
         * @inheritDoc
         */
        public function set listData(value:BaseListData):void
        {
            if (value == _listData)
                return;
            _listData = value;
            dispatchEvent(new Event("listDataChanged"));
        }
    ]]>
    </mx:Script>
    <mx:Label fontWeight="bold" text="{listData.label}" />
    <mx:Label text="{data.firstName + ' ' + data.lastName}" />
</mx:HBox>

score -1 · Answer 3 · answered Aug 02 '11 at 12:06

Item renderer has an item index property on it.

this.itemIndex

Sample:

<s:List>
        <s:dataProvider>
            <s:ArrayList>
                <fx:String>Item 1</fx:String>
                <fx:String>Item 2</fx:String>
                <fx:String>Item 3</fx:String>
                <fx:String>Item 4</fx:String>
                <fx:String>Item 5</fx:String>
                <fx:String>Item 6</fx:String>
            </s:ArrayList>
        </s:dataProvider>
        <s:itemRenderer>
            <fx:Component>
                <s:ItemRenderer>
                    <s:HGroup>
                        <s:Label text="This index is: {this.itemIndex}" />
                        <s:Label text="{data}" />
                    </s:HGroup>
                </s:ItemRenderer>
            </fx:Component>
        </s:itemRenderer>
    </s:List>

Display List ItemRenderer Index in Flex3

3 Answers3

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