Printing with Documents and Views
MFC's print architecture is built around a kernel formed by GDI printing functions and virtual CView member functions. To understand what's on the outside, it helps to first understand what's on the inside. Here's the approach we'll take in this chapter as we study the code that enables an MFC application to support printing and print previewing:
- Look at the Windows printing model, and examine the steps an SDK-style application goes through to print a document.
- Understand the relationship between the Windows print architecture and the MFC print architecture and the mechanics of printing from MFC applications.
- Develop a bare-bones printing program that demonstrates how the same code can be used to send output to either the screen or the printer.
- Develop a more ambitious printing program whose printing and previewing capabilities are on a par with those of commercial applications.
As you'll discover, printing from an MFC application isn't altogether different than rendering to the screen except for the fact that printed output must be paginated. Because MFC handles almost everything else, much of the effort you expend writing printing code will be devoted to figuring out where the page breaks go and how to position your output on the printed page.
The Windows Print Architecture
Printing a document from a Windows application without the benefit of MFC involves a number of steps. You begin by obtaining a device context (DC) for the printer that output will go to. Just as an application needs a screen DC to send output to the screen, it needs a printer DC to send output to a printer. If you know the device name of the printer you want to print to, you can create a device context yourself with the Win32 ::CreateDC function or MFC's CDC::CreateDC:
CDC dc;dc.CreateDC (NULL, _T ("HP LaserJet IIP"), NULL, NULL);If you don't know the device name but would like the application to print to the default printer, you can use MFC's handy CPrintDialog::GetDefaults and CPrintDialog::GetPrinterDC functions to create the device context:
CDC dc;CPrintDialog dlg (FALSE);dlg.GetDefaults ();dc.Attach (dlg.GetPrinterDC ());
If you'd like to let the user select a printer, you can use CPrintDialog::DoModal to display a Print dialog (one of the common dialogs supplied by the operating system) and call CPrintDialog::GetPrinterDC to get a DC after the dialog is dismissed:
CDC dc;CPrintDialog dlg (FALSE);if (dlg.DoModal () == IDOK)
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