How to access and control a checkbox that's inside a style?

Question

I have a style for list box items which contains a checkbox. For every list box item, there is a property called isChecked that I can read and write to just fine, but it does not influence the checkbox in the style. Any idea how to make the checkbox synchronize with the isChecked property?

Here's the style structure:

Answer 1

Just found out list box contains a boolean property named "ShowCheckboxes"...