silverlight - Binding position to ActualHeight -

I want to paste the status of a list into XAML at its height. Therefore its bottom left corner always be at the canvas 0.0. I'm using the element the actual height to get the binding and a convertor to overturn the property. But the height sent to the converter is 0.

How do I solve it or am I going wrong on this?

  & lt; Canvas x: name = "display surface" & gt; & Lt; ListBox x: Name = "MenuList" visibility = "visible" canvas. Tap = "{binding element name = menu list, path = real high, converter = {static resource lamda convent}, converter parameter = 'val => gt; -val'}" & gt; & Lt; ListBoxItem content = "item 1" /> & Lt; ListBoxItem Content = "Item 2" /> & Lt; ListBoxItem content = "item 3" /> & Lt; ListBoxItem Content = "Item 4" /> & Lt; ListBoxItem content = "item5" /> & Lt; ListBoxItem Content = "Item 6" /> & Lt; / ListBox & gt; & Lt; / Canvas & gt;  
 
 binding  {binding active high, relative sours = {relative esc safe} Try, convertor = {static resource Lambda convent}, converter parameter = 'val =' -val '}