How to bind item values in an accordion header template

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C#

Silverlight

templates

I'm trying to create a simple header template for an accordion object in silverlight 4. I've added an image and a TextBlock to the header template of the AccordionItem.
I want to hide or show the image dependant on the values entered on the page. Because i want to bind these values directly to the actual accordion item, I've created a new type 'AccordionItemWithIcons' that simply inherits from AccordionItem but adds a couple of dependancy properties to handle this. I'm only showing a couple of those properties for brevity. :)

So, here's my accordion with my 'AccordionItemWithIcons' control. Note that the property 'CheckIsVisible' is of type 'Visibility'

<grid x:name="LayoutRoot" xmlns:x="#unknown">
    <controls:accordion height="100" xmlns:controls="#unknown">
        <my:accordionitemwithicons xmlns:my="#unknown">
            x:Name="FirstItem"
	    Content="Content Text" 
	    Header="Header Text" 
    	    CheckIsVisible="Collapsed" 
    	    EventSummary="Summary Text" 
    	    HeaderTemplate="{StaticResource AccordionItemHeaderTemplate1}"/>
    </my:accordionitemwithicons></controls:accordion>
</grid>

And here is the header template.

<datatemplate x:key="AccordionWithIcons_HeaderTemplate1" xmlns:x="#unknown">
    <grid>        	
        <stackpanel orientation="Horizontal" verticalalignment="Top">
            <textblock text="{Binding EventSummary}" />
            <Image Visibility="{Binding CheckIsVisible}" Source="/cross.png"/>
        </stackpanel>
    </grid>
</datatemplate>

Can anyone explain how I can bind the TextBlock's text and the Image's Visibility to the values set in the underlying AccordionItemWithIcons object?

I don't know if helps to explain what I'm trying to achieve, but ultimately in the code behind i want to be able to say something like (shown below), to show or hide the icon in the header template.

FirstItem.CheckIsVisible = Visibility.Visible
SecondItem.CheckIsVisible = Visibility.Collapsed
...etc...