How to prevent an applet from being silently closed (with unsaved data)

It is generally a good idea to ask the user before closing an application without saving the data. If you deploy an applet, the situation is even worse: the user may get distracted, follow some link, forget what he was doing, and close the whole browser without realizing he closed the applet too. Fortunately, it's very simple to tell the browser to display a warning. Before closing a page for any reason (reload, closing the tab, close the browser, ...), a "modern" browser will call window.onbeforeunload. If you want to alert the user, you simply need to create a javascript function that calls your applet and returns the warning message. Here is an example. This is an applet with a checkbox and a textfield. Note the two methods isPreventClose() and getPreventCloseMessage(), which define whether the applet needs to block the closing of the page and what message to prompt. package test.applet; public class MyApplet extends javax.swing.JApplet { @Override public void init() { try { java.awt.EventQueue.invokeAndWait(new Runnable() { public void run() { initComponents(); } }); } catch (Exception ex) { } } // To be called in javascript public boolean isPreventClose() { return preventClose.isSelected(); } // To be called in javascript public String getPreventCloseMessage() { ...

Date: September, 27 2010
Url: http://www.java.net/blog/carcassi/archive/2010/09/27/how-prevent-applet-being-silently-closed-unsaved-data

Others News