public static void RegisterFrame(Frame frame, String sessionStateKey)
{
if (frame.GetValue(FrameSessionStateKeyProperty) != null)
{
throw new InvalidOperationException("Frames can only be registered to one session state key");
}
if (frame.GetValue(FrameSessionStateProperty) != null)
{
throw new InvalidOperationException("Frames must be either be registered before accessing frame session state, or not registered at all");
}
// Use a dependency property to associate the session key with a frame, and keep a list of frames whose
// navigation state should be managed
frame.SetValue(FrameSessionStateKeyProperty, sessionStateKey);
_registeredFrames.Add(new WeakReference<Frame>(frame));
// Check to see if navigation state can be restored
RestoreFrameNavigationState(frame);
}
