Unsolicited About Boxes

Q:  My Java application has an ApplicationListener with a handleAbout() method, but the default about box still appears over my own when "About MyApp" is selected from the Application menu. Why?

A: Important:

This Q&A refers to the eAWT APIs that were introduced with Java 1.4.1 on Mac OS X. These APIs were deprecated in Java SE 6 and J2SE 5.0 with the release of "Java for Mac OS X 10.6 Update 3" and "Java for Mac OS X 10.5 Update 8".

Please use the Application.setAboutHandler(AboutHandler) and Application.setQuitHandler(QuitHandler) which do not require explicit event overriding by design.

The problem is that the ApplicationEvent received by handleAbout() needs to marked as handled; otherwise the eAWT does not know if you have actually handled the request. This is stated in the eAWT javadocs, but commonly overlooked.

Below is a simplified example of a proper handleAbout method. Note that at the end of the method, a call to ApplicationEvent.setHandled(true) is made. Without this call, the eAWT will assume that you have not actually handled the event and will put up its own default about box.

Listing 1  Suppressing the default aboutBox using setHandled(true).

public void handleAbout(ApplicationEvent e) {

   new AboutBox().show();

   // Tell eAWT you've handled the request, disabling the default about box.

   e.setHandled(true);

}

A similar problem may occur with the handleQuit method; in this case, you actually call ApplicationEvent.setHandled(true) to allow the application to quit. In other words, you have successfully handled the quit request and are ready for the default handler to continue.

Listing 2  Authorizing a quit using setHandled(true).

public void handleQuit(ApplicationEvent e) {

   cleanupResources();

   // The quit request is handled; proceed with app termination

   e.setHandled(true);

}

If you wish to have complete control over the quit and call System.exit() yourself, for example, set the event's state to false in your handleQuit method. Note that although the default handled state of an ApplicationEvent is false, we still recommend setting the state explicitly to ensure the behavior you want.

Listing 3  Rejecting a quit using setHandled(false).

public void handleQuit(ApplicationEvent e) {

   // Reject the quit request and handle it as we see fit

   e.setHandled(false);

   String msg = "Are you sure you want to quit?"

   int result = JOptionPane.showConfirmDialog(mainFrame, msg);

   if (result == JOptionPane.YES_OPTION) {

      System.exit(0);

   }

}

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