How to bind to the AutomationId attached property?

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C#

.NET

WPF

UI

automation

.NET4.5

I can not bind to the AutomationId property.
I need to add AutomationId property to a custom control that contains, among other controls, a textbox.
The custom control is instantiated in a list view so it is present in several Items.
In order to provide a unique AutomationId for the textbox I computed its value as a concatenation of the textbox name and the AutomationId property of the custom control instance it belongs to.
The custom control instance AutomationId is itself computed with a binding to the AutomationId of the ListViewItem where it is instantiated which includes the item index.

Snooping through the tree I can see that the AutomationId of the custom control is computed correctly but the AutomationId of the contained TextBox is not.
Debugging the binding using a converter I could see that the AutomationId property of the custom control is an empty string when it is used by the TextBox to compute its AutomationId.

How can i solve this problem?
Generally speaking, in cases where we have a dynamic control defined inside a custom control which is itself instantiated in a dynamic control, how to proceed with the automationId setting in the inner controls?
Thanks in advance,
Pietro