<?xml version="1.0" encoding="utf-8"?>
<!-- http://blog.flexexamples.com/2008/08/08/setting-a-specific-number-of-rows-in-a-tilelist-control-in-flex/ -->
<mx:Application name="TileList_rowCount_test"
        xmlns:mx="http://www.adobe.com/2006/mxml"
        layout="vertical"
        verticalAlign="middle"
        backgroundColor="white">

    <mx:Script>
        <![CDATA[
            import mx.events.SliderEvent;

            private function slider_change(evt:SliderEvent):void {
                tileList.rowCount = evt.value;
            }
        ]]>
    </mx:Script>

    <mx:ArrayCollection id="arrColl">
        <mx:source>
            <mx:Array>
                <mx:Object label="One" />
                <mx:Object label="Two" />
                <mx:Object label="Three" />
                <mx:Object label="Four" />
                <mx:Object label="Five" />
                <mx:Object label="Six" />
                <mx:Object label="Seven" />
                <mx:Object label="Eight" />
                <mx:Object label="Nine" />
                <mx:Object label="Ten" />
            </mx:Array>
        </mx:source>
    </mx:ArrayCollection>

    <mx:ApplicationControlBar dock="true">
        <mx:Form styleName="plain">
            <mx:FormItem label="rowCount:">
                <mx:HSlider id="slider"
                        minimum="1"
                        maximum="3"
                        value="3"
                        snapInterval="1"
                        tickInterval="1"
                        liveDragging="true"
                        change="slider_change(event);" /> 
            </mx:FormItem>
        </mx:Form>
    </mx:ApplicationControlBar>

    <mx:TileList id="tileList"
            dataProvider="{arrColl}"
            columnCount="4"
            columnWidth="100"
            rowCount="3"
            rowHeight="50"
            verticalScrollPolicy="on" />

</mx:Application>