Flex ItemRender Not Updating Data Source - actionscript-3

Question

First up sorry the the mass of code and terrible coding, it's been some time since I have done AS3/Flex and for the life of me I can't remember how to get an ItemRenderer inside an ItemRender to update the data source. For example GymButton2.mxml simple adds +1 to the data it it provided with when a button is clicked and this should update the original datasource activeGym but... it doesn't and I assume this is because binding is not working as expected?
Main.mxml
<fx:Script>
<![CDATA[
import mx.collections.ArrayCollection;
import mx.events.FlexEvent;
[Bindable]
public var activeGym:Gym2;
]]>
</fx:Script>
<s:DataGroup x="33" y="56" width="200" height="200" dataProvider="{activeGym.sets}" itemRenderer="GymSetRenderer">
<s:layout>
<s:VerticalLayout />
</s:layout>
</s:DataGroup>
</s:WindowedApplication>
Gym2.as
package
{
import flash.events.EventDispatcher;
import flash.events.IEventDispatcher;
import mx.collections.ArrayCollection;
[Bindable]
public class Gym2 extends EventDispatcher
{
public var sets:ArrayCollection = new ArrayCollection();
public function Gym2(target:IEventDispatcher=null)
{
super(target);
}
public function addSet(set:GymSet):void {
sets.addItem(set);
}
}
}
GymSetRenderer.mxml
<?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"
autoDrawBackground="false" xmlns:local="*">
<s:layout>
<s:VerticalLayout />
</s:layout>
<s:Label fontSize="27" text="{data.title}"/>
<s:DataGroup dataProvider="{data.data}" itemRenderer="GymButton2">
<s:layout>
<s:HorizontalLayout />
</s:layout>
</s:DataGroup>
</s:ItemRenderer>
GymButton2.mxml
<?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" autoDrawBackground="true">
<fx:Script>
<![CDATA[
protected function onClick(event:MouseEvent):void
{
data = data + 1;
}
]]>
</fx:Script>
<s:Button label="{data}" height="70" click="onClick(event)"/>
</s:ItemRenderer>