PrintHookProc

The PrintHookProc hook procedure is an application-defined or library-defined callback function that is used with the PrintDlg function. The function receives messages or notifications intended for the default dialog box procedure of the Print common dialog box.

The LPPRINTHOOKPROC type defines a pointer to this callback function. PrintHookProc is a placeholder for the application-defined or library-defined function name.

UINT CALLBACK PrintHookProc(
  HWND hdlg,      // handle to the dialog box window
  UINT uiMsg,     // message identifier
  WPARAM wParam,  // message parameter
  LPARAM lParam   // message parameter
);
 

Parameters

hdlg

Handle to the Print common dialog box window for which the message is intended.

uiMsg

Identifies the message being received.

wParam

Specifies additional information about the message. The exact meaning depends on the value of the uiMsg parameter.

lParam

Specifies additional information about the message. The exact meaning depends on the value of the uiMsg parameter.

If the uiMsg parameter indicates the WM_INITDIALOG message, lParam is a pointer to a PRINTDLG structure containing the values specified when the common dialog box was created.

Return Values

If the hook procedure returns zero, the default dialog box procedure processes the message.

If the hook procedure returns a nonzero value, the default dialog box procedure ignores the message.

Remarks

When you use the PrintDlg function to create a Print common dialog box, you can provide a PrintHookProc hook procedure to process messages or notifications intended for the dialog box procedure. To enable the hook procedure, use the PRINTDLG structure that you passed to the dialog creation function. Specify the address of the hook procedure in the lpfnPrintHook member and specify the PD_ENABLEPRINTHOOK flag in the Flags member.

The default dialog box procedure processes the WM_INITDIALOG message before passing it to the hook procedure. For all other messages, the hook procedure receives the message first. Then, the return value of the hook procedure determines whether the default dialog procedure processes the message or ignores it.

If the hook procedure processes the WM_CTLCOLORDLG message, it must return a valid brush handle for painting the background of the dialog box. In general, if the hook procedure processes any WM_CTLCOLOR* message, it must return a valid brush handle for painting the background of the specified control.

Do not call the EndDialog function from the hook procedure. Instead, the hook procedure can call the PostMessage function to post a WM_COMMAND message with the IDABORT value to the dialog box procedure. Posting IDABORT closes the dialog box and causes the dialog box function to return FALSE. If you need to know why the hook procedure closed the dialog box, you must provide your own communication mechanism between the hook procedure and your application.

You can subclass the standard controls of the common dialog box. However, the common dialog box procedure may also subclass the controls. Because of this, you should subclass controls when your hook procedure processes the WM_INITDIALOG message. This ensures that your subclass procedure receives the control-specific messages before the subclass procedure set by the dialog box procedure.

QuickInfo

  Windows NT: Requires version 3.1 or later.
  Windows: Requires Windows 95 or later.
  Windows CE: Requires version 2.0 or later.
  Header: Declared in commdlg.h.
  Import Library: User-defined.

See Also

Common Dialog Box Library Overview, Common Dialog Box Functions, EndDialog, PostMessage, PrintDlg, PRINTDLG, WM_INITDIALOG, WM_CTLCOLORDLG