Custom Dialog Boxes
An application can create custom dialog boxes by using an application-defined
window class for the dialog boxes instead of using the predefined dialog box
class. Applications typically use this method when a dialog box is their main
window, but it is also useful for creating modal and modeless dialog boxes for
applications that have standard overlapping windows.
The application-defined window class allows the application to define a window
procedure for the dialog box and process messages before sending them to the
dialog box procedure. It also lets the application define a class icon, a class
background brush, and a class menu for the dialog box. The application must
register the window class before attempting to create a dialog box and must
provide the dialog box template with the atom value or name of the window class.
Many applications create a new dialog box class by first retrieving the class
information for the predefined dialog box class, and passing it to the
GetClassInfo function, which fills a
WNDCLASS structure with the information. The application modifies individual members
of the structure, such as the class name, brush, and icon, then registers the
new class by using the
RegisterClass function. If an application fills the
WNDCLASS structure on its own, it must set the
cbWndExtra member to the DLGWINDOWEXTRA, which is the number of extra bytes Windows
requires for each dialog box. If an application also uses extra bytes for each
dialog box, they must be beyond the extra bytes required by Windows.
The window procedure for the custom dialog box has the same parameters and
requirements as any other window procedure. Unlike other window procedures,
however, the window procedure for this dialog box should call the
DefDlgProc function instead of the
DefWindowProc function for any messages it does not process.
DefDlgProc carries out the same default message processing as the window procedure for
the predefined dialog box, which includes calling the dialog box procedure.
An application can also create custom dialog boxes by subclassing the window
procedure of the predefined dialog box. The
SetWindowLong function lets an application set the address of the window procedure for a
given window. The application may also attempt to subclass by using the
SetClassLong function, but doing so affects all dialog boxes in the system, not just those
belonging to the application.
Applications that create custom dialog boxes sometimes provide an alternate
keyboard interface for the dialog boxes. For modeless dialog boxes, this may mean
the application does not call the
IsDialogMessage function and instead processes all keyboard input in the custom window
procedure. In such cases, the application can use the
WM_NEXTDLGCTL message to minimize the code needed to move the input focus from one control
to another. This message, when passed to
DefDlgProc, moves the input focus to a specified control and updates the appearance of
the controls, such as moving the default push button border or setting an
automatic radio button.
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