A dialog box is a special type of window for use in certain circumstances where an additional interaction with the user is required. Dialog boxes may be of two distinct types; modal or modeless.
A dialog box is created as a short-lived window to receive and/or display a particular set of information required for the correct performance of an action by the application.
With a modal dialog box, the user may not interact with another window until the dialog is complete. This modality may be within an application (preventing interaction with other windows controlled by this application program, while allowing interaction with other applications in the system) or system-wide (preventing interaction with any other window until the dialog is complete).
With a modeless dialog box, the user may continue to work with the primary application window, for example using the "Find" window with the OS/2 System Editor. Modeless dialogs are preferred by CUA.
One difference between a dialog box and a standard window is that the dialog box may not be sized on the screen, nor may it be maximized or minimized except in certain circumstances. This property of a dialog box is crucial in maintaining the integrity of the dialog with the end user. Note that although a dialog box is not sizable, it may be moved on the desktop.
An example of a dialog box is shown in Figure "Presentation Manager Dialog Box".
For example, if a user selects "Open" from the "File" pull-down menu, the application requires the name of the file before it can be opened; this information will be requested using a modal dialog box. For confirmation with the user, a message box may be used as an alternative to a dialog box; see Message Boxes for further information.