BeforePrint

My Script is below:

#targetengine "session"

main();

function main(){

    var myApplicationEventListener = app.eventListeners.add("beforePrint",myEventInfo);

    }

function myEventInfo(myEvent){

    alert("Yes");

    }

I can popup the message box, while i'm print the doc, but when I get document into a book, then I use print book or print selected document, can't popup a message box, how can I even popup the message box even I print the book or print the selected document???