title: WPF binding to a global variable to update UI
body: <p>Let's say I have two windows and a trayicon context menu.  Each of the windows has a togglebutton and the context menu has a checkable menu item.  All three controls are designed to display and toggle the status of the same value.  </p>
  
  <p>How can I bind, in this case IsChecked, of the three controls to a single global variable that when one of the controls is checked/unchecked that the other controls will update accordingly?  Should I just do an invoke or is there an MVVM solution?  I'm new to WPF so I'm not sure the best/most correct way to accomplish this.</p>