title: How to create Tri-state CheckBox that summarize state of all CheckBoxes in a ListView?
body: <p>I have a WPF <code>ListView</code> that contains <code>CheckBox</code> column and other columns of the custom object. I want to put another <code>CheckBox</code> over this <code>ListView</code>--tri-state <code>CheckBox</code>--so its state will be binded to the checked checkboxes. If everyone is checked the state of upper checkbox will be checked. If only some of them the state will be indeterminate. Otherwise its state will be unchecked. (like in Gmail)</p>