reference manager

Hi thank you for reading my question , 

Im new to coding

at the moment , i have something like if a condition is fullfilled a messagebox pops out .

to avoid it popping out repeatedly, im doing something like

private int Index = 0;

if (IsLastBar & IsRealTime & Index != index)
                        {
                            MessageBox.Show( );

                            Index = index;

}

my problem is if i am using several indicators e.g. 4,  at the same time (like they are in different public class )  if their condition is fulfilled at the same time i would have got 4 message boxes popping out ,

without having to put all of them together in one indicator , is it possible for me to make another indicator that specifically does this (Index = index) thing for all of them, as a group, linking them through reference manager ,  so only one message box popped out between the start and end of each bar 

Thank you very much 

Henry