private static void RemoveHandler(IInvocation invocation)
 {
     ((INotifyPropertyChanged)invocation.GetCurrentValue()).PropertyChanged -=
         Handlers[invocation.InvocationTarget][invocation.PropertyName()];
     Handlers.Remove(invocation.InvocationTarget);
 }
 static void RemoveHandler(IInvocation invocation)
 {
     (invocation.GetCurrentValue() as INotifyPropertyChanged).PropertyChanged -= handlers[invocation.InvocationTarget][invocation.PropertyName()];
     handlers.Remove(invocation.InvocationTarget);
 }