如何关闭用作WPF中子菜单的Popup

I have a button that when clicked opens a Popup. The Popup is a sub-menu containing more buttons. When one of the buttons on the sub-menu are clicked the Popup closes. I also want the Popup to close when the user clicks somewhere outside the Popup. It's also important to note that the majority of the screen is taken up by a WindowsFormsHost that displays an OpenGL Win Forms control.I have a button that when clicked opens a Popup