How to catch user leaving a page and cancelling it

Question

When a user leaves the GWT app, I would like to open a confirm dialog and offer them the choice to stay, i.e. Confirm(\"are you sure you want to leave this page\", \"yes\",

Answer 1

Call Window.addWindowClosingHandler, and pass it a callback that calls setMessage on the Window.ClosingEvent, like so:

Window.addWindowClosingHandler(new Window.ClosingHandler() {
      public void onWindowClosing(Window.ClosingEvent closingEvent) {
        closingEvent.setMessage("Do you really want to leave the page?");
      }
    });

(I've put in links to the GWT 2.0 docs; change the 2.0 to 1.6 in those URLs to see the GWT 1.6/1.7 docs.)

Note that doing it this way, you don't have to/don't get to create the dialog box yourself.