Standard File Open dialog with preview

This article describes a completely object oriented standard file open dialog with preview. No custom hook function, just common MFC message maps. The dialog has a CDibStatic member, which displays the preview image when available. The CDibStatic class encapsulates a static control that displays images and is described in an article in the static controls section.

This is how the dialog looks like:

The template for the dialog is a normal developer studio dialog template. Note however, the use of the stc32 static control. As it hasn't any text in it, it is invisible unless you select it. This static control will serve as a place holder for the standard file dialog controls, thus establishing the position of the newly added controls in respect to the standards. If there is no stc32 control specified in the template, all the new controls will be placed below the standard controls. Otherwise, the common file dialog will look at the size of the stc32 control to attempt to fit all the standard controls in it. If it is not big enough, it is resized to make room for the standard controls, and then the new controls are repositioned with respect to the resized stc32 control.

Palette support is included within the dialog class. It is implemented using handlers for the WM_QUERYNEWPALETTE and WM_PALETTECHANGED windows messages, so you have to ensure in your program that the dialog receives these messages. If the palette never changes, the image is painted with the right palette selected the first time. Since the standard dialogs are modal, the palette changes can be due only to other applications (unless you change it in another thread), thus realizing palette when gaining focus should always maintain the right colors. You can realize the palette at any time you wish by sending a WM_QUERYNEWPALETTE message to the CDibStatic control, for instance.

This class has been used (among other things) to implement a completely object oriented DIBLOOK. This article can be found in the samples section.

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Date Last Updated: April 3, 1999