How do I determine if a WPF window is modal?

http://stackoverflow.com/questions/368926/how-do-i-determine-if-a-wpf-window-is-modal

http://stackoverflow.com/questions/5093899/close-all-open-modal-dialog-windows

 

System.Windows.Interop.ComponentDispatcher.IsThreadModal

But if show MessageBox or other native dialog, this API is unhelp.