Modal window

• Drawing attention to vital pieces of information. This use has been criticized as ineffective because users are bombarded with too many dialog boxes, and habituate to simply clicking "Close", "Cancel", or "OK" without reading or understanding the message.[6]^[7][8]
• Blocking the application flow until information required to continue is entered, as for example a
  login process. Another example are file dialogs
  to open and save files in an application.
• Collecting application configuration options in a centralized dialog. In such cases, typically the changes are applied upon closing the dialog, and access to the application is disabled while the edits are being made.
• Warning that the effects of the current action are not reversible. This is a frequent interaction pattern for modal dialogs, but some usability experts criticize it as ineffective for its intended use (protection against errors in destructive actions) due to habituation. They recommend making the action reversible (providing an "undo" option) instead.^[1]

Modal sheets in Mac OS X

Many features that would typically be represented by modal windows are implemented as modal transient panels called "Sheets"^[9] on Mac OS X. Transient windows behave similarly to modal windows – they are always on top of the parent window and are not shown in the window list, but they do not disable the use of other windows in the application. Sheets slide out of the window's title bar, and usually must be dismissed before the user can continue to work in the window, but the rest of the application stays usable. Thus they create a mode inside the window that contains them, but are modeless with respect to the rest of the application.

Control of interaction flow

Modal windows are common in GUI toolkits for guiding user workflow. Alan Cooper contends that the importance of requiring the user to attend to important issues justifies restricting the user's freedom and that the alternative would increase user frustration.^[10]

Unexpected interruptions

Unexpected

One proposed approach is to design every input element as a self-contained, task-oriented interaction, guided by its own specific requirements rather than by the global state of the entire application. For example, required elements might be preceded with an asterisk, elements with invalid data might acquire a red border, and so on. With this approach, users actually benefit from seeing many input elements at once — they can enter data in a way that makes sense to them, instead of having all the other unrelated elements blocked until a predefined data-entry sequence is completed.

Problems

A modal window blocks all other

However, many interface designers have recently taken steps to make modal windows more obvious by darkening the background behind the window or allowing any mouse click outside of the modal window to force the modal window to close – a design called a Lightbox^[5] – thus alleviating those problems. Jakob Nielsen states as an advantage of modal dialogs that it improves user awareness: "When something does need fixing, it's better to make sure that the user knows about it." For this goal, the Lightbox design provides strong visual contrast of the dialog over the rest of the visuals. The Lightbox technique is now a common tool in website design.

Modal windows are commonly implemented in ways that block the possibility to move, minimize, iconify, or push that window back, and they grab input focus, which often prevents use of a system's cut, copy, and paste facilities. This can interfere with the use of their parent applications by blocking access to other windows and data within the same application, particularly in cases where the modal window is requiring the user to input information only available in one of the windows it's covering.

For users using virtual work areas larger than their actual screens, modal windows can cause further undesirable behavior, including creating the modal on a portion of the virtual screen not currently on the display, or abruptly switching the display from what the user was working on to an entirely different section.

Modal windows tend to create an abrupt diversion of text input, especially typed input intended for other programs, into themselves. Further, modals usually interpret actuation of the enter key (or in rare cases the presence of a newline in pasted input) as a cue to accept the input and process it—or, in rare cases, may intercept a mouse click intended for a different application that has suddenly been covered. Such interception, called focus stealing (or stealing focus) can compromise privacy and security practices, as well as capture inappropriate, out-of-context input that can cause undefined, arbitrary results in the program that generated the modal window.

Depending on the specifics of implementation, modal windows can violate the

Recommendations

Modal dialogs are part of a task flow, and recommendations are given to place them where the focus is in that flow. For example, the window could be placed near the

• Application posture
• Popover (GUI)

References