A modal dialog window is a message that pops up in front of your screen, and prevents you from continuing with your task until you've dealt with it. One example is a version of the Windows XP shutdown dialog, shown to the left. Users get here by choosing Start > Shut Down. Potentially, if they Shut Down accidentally, unpleasant consequences could result, so this dialog is designed to prevent accidents. It also surfaces related options (Logoff, Suspend, Restart, etc.) that may not appear at the initial level.
Contrast this solution with the pictured Macintosh OS X Leopard shutdown dialog. Instead of requiring a user action to confirm the shutdown, the system counts down before shutdown. A button is provided to skip the countdown, but users could simply walk away after the single command to shut down, and consider their task complete. The designer discusses this feature's design at length in his blog, contrasting it with the Windows XP and Vista solutions.
Modal dialogs proliferate online, not just in operating systems. The lightbox style modal dialog, where the browser dims the page behind the dialog, is popular in web applications.
Problems with modal dialogs include:
- Users habituate to dismissing them quickly, so they don't offer protection.
- They may be hidden behind other windows. (I have this problem frequently with Adobe Acrobat's print dialog.)
- They slow users down. In many cases, a better design would achieve the same goals without slowing users.
Firefox 3 and Google Chrome have killed the "Remember my login" modal dialog with its new browser bar implementation. Contrast this bar with Internet Explorer 7, which takes over the screen and requiring users to immediately decide -- save password or not?
This is great because it keeps users immersed in their activity. Remembering the password is a useful feature, but it's still optional. The browser bar surfaces the feature at the correct time without requiring users to stop everything and service it.
If you're building web applications, kill your modal dialogs for asking permission. Google Gmail, for example, foregoes delete confirmation and provides a link to undo your delete. Undo is better than Are You Sure?