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<META NAME="Author" CONTENT="Zafir Anjum">
<TITLE>MFC Programmer's SourceBook : Printing</TITLE>
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Print Previewing without the Document/View Framework
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<!-- Author and contact details -->
This article was contributed by <A HREF="mailto:koaykh@tm.net.my">Koay Kah Hoe</A>.
<!-- Text / source code -->
<P>Thanks to
<A HREF="mailto:chrismaunder@codeguru.com">Chris Maunder</A>
for introducing the printing method in
<A HREF="http://www.codeguru.com/printing/printing_wo_docview.shtml">Printing without the Document/View framework</A>.
Many people have been asking for print preview without the doc/view framework as well. However, so far, no body has
proposed a way to do that in this column yet. (Except for the unknown 'm_bPrintPreview' suggestion, but seems that there
is no such a free ticket.) I have studied on how Microsoft implements print preview in doc/view framework using the class
CPreviewView, which is derived from CSrollView. The print preview is called from CView::OnFilePrintPreview( ) and
CView::DoPrintPreview. They are undocumented, the source code can be found from VC\mfc\src\Viewprev.cpp. The implementation
relies on CView and CFrameWnd framework extensively.
<P>In order to use the default print preview functionality in non doc/view framework, like dialog based applications,
I played a trick by creating temporary CFrameWnd and CView objects and then call the default OnFilePrintPreview( ) from the
temporary view class. I've borrowed
<A HREF="mailto:chrismaunder@codeguru.com">Chris Maunder</A>'s
CGridCtrl control from
<A HREF="http://www.codeguru.com/controls/gridctrl.shtml">MFC Grid control (derived from CWnd)</A> article
as an example to illustrate the implementation. The code was developed under VC5 environment and have been tested in
Windows 98 and NT platform without any problem. :)
<!-- Sample image - gif or jpg -->
<P><IMG SRC="preview.jpg" >
<H4>To do:</H4>
<P>Add a function PrintPreview( ) in your control class (CGridCtrl in this case) or the class where you put your
OnBeginPrinting, OnPrint, etc. Also, add two member variables to the class and initialize them:
<!-- start a block of source code -->
<PRE><TT><FONT COLOR="#990000">
// In your header file /////////////
private:
CSingleDocTemplate* m_pTemplate;
public:
BOOL m_bPrintPreview;
void PrintPreview();
////////////////////////////////////
// In your class constructor ///////
#include "ViewPrintPreview.h"
CGridCtrl::CGridCtrl(...)
{
// Add initialization
m_pTemplate=NULL;
m_bPrintPreview=FALSE;
}
////////////////////////////////////
// In your class ///////////////////
void CGridCtrl::PrintPreview()
{
if (m_bPrintPreview)
{
AfxGetApp()->m_pMainWnd->SetFocus();
return;
}
CFrameWnd* pOldFrame=(CFrameWnd*)AfxGetThread()->m_pMainWnd;
if (!m_pTemplate)
{
m_pTemplate = new CSingleDocTemplate(
IDR_MENU,
NULL,
RUNTIME_CLASS(CFrameWnd),
RUNTIME_CLASS(CViewPrintPreview));
AfxGetApp()->AddDocTemplate(m_pTemplate);
}
CFrameWnd * pFrameWnd = m_pTemplate->CreateNewFrame( NULL, NULL );
m_bPrintPreview=TRUE;
m_pTemplate->InitialUpdateFrame( pFrameWnd, NULL);
CViewPrintPreview* pView=(CViewPrintPreview*)pFrameWnd->GetActiveView();
pView->m_pCtrl=this;
pView->m_pOldFrame=pOldFrame;
AfxGetApp()->m_pMainWnd=pFrameWnd;
pFrameWnd->SetWindowText(_T("Koay Kah Hoe Print Preview"));
pFrameWnd->ShowWindow(SW_SHOWMAXIMIZED);
pView->OnFilePrintPreview();
}
<!-- end the block of source code -->
</FONT></TT></PRE>
<P>A CSingleDocTemplate object is used to create a frame and a view window. The view class CViewPrintPreview has no chance
to show itself, as it is suppressed by preview view immediately. The m_pMainWnd pointer is changed to the new CFrameWnd
so that the preview class can use it as parent frame. (Has any one do this before?) The original m_pMainWnd is saved in
the view class, when preview is ended, it will restore the pointer back to original value. Then, OnFilePrintPreview is
called.
<P>Add the view class CViewPrintPreview and its header file to the project. The main job of the view class is to pass the
printing functions OnBeginPrinting, OnPrint and OnEndPrinting to the control class or wherever you place them. This must
be done through view class as the print preview calls these functions from view class. When the preview window is closed,
the program must restore the m_pMainWnd pointer back to its original value. Then, the frame and view window must be
destroyed. This is done in the function OnEndPrintPreview.
<P>Now, you can view the preview window already. However, this is not the end of the story yet, the toolbar buttons cannot
update themselves as normally them should be. After some investigation, I found that the window normally calls the message
WM_IDLEUPDATECMDUI to update the toolbar's state from the OnIdle function in SDI or MDI application. For dialog based
application, the OnIdle function is not called. Thus, the message WM_IDLEUPDATECMDUI is not sent to update toolbar. We have
to send the message ourselves. I overrided the virtual function ContinueModal( ) in the main dialog class to do the job:
<!-- start a block of source code -->
<PRE><TT><FONT COLOR="#990000">
BOOL CGridCtrlDemoDlg::ContinueModal()
{
if (m_Grid.m_bPrintPreview) // m_Grid is your control class
// send WM_IDLEUPDATECMDUI message to update toolbar state
// This is normally called by OnIdle function in SDI or MSI applications.
// Dialog based applications don't call OnIdle, so send the message from here instead
AfxGetApp()->m_pMainWnd->SendMessageToDescendants(WM_IDLEUPDATECMDUI,
(WPARAM)TRUE, 0, TRUE, TRUE);
return CDialog::ContinueModal();
}
<!-- end the block of source code -->
</FONT></TT></PRE>
<P>Special precaution has to be taken when you use the print preview. As a new window is created for print preview, the
main dialog or control is still accessible by the user. When a preview window is opened, changes made at the main dialog
or control could reflect to the preview window causing some unexpected result. You might need to disable any editing while
previewing by referring to the public Boolean variable m_bPrintPreview. Another thing is, as the m_pMainWnd pointer is
pointed to the new frame window when doing preview, elsewhere in your application that uses this pointer could cause your
program to crash. Again, you can use the m_bPrintPreview as an indicator to determine which window the m_pMainWnd is
pointed to.
<P>Finally, I wish you happy previewing! :)
<BR><BR><BR>
<h4>ViewPrintPreview header file:</h4>
<!-- start a block of source code -->
<PRE><TT><FONT COLOR="#990000">
#if !defined(AFX_VIEWPRINTPREVIEW_H__137FC880_1607_11D3_9317_8F51A5F9742F__INCLUDED_)
#define AFX_VIEWPRINTPREVIEW_H__137FC880_1607_11D3_9317_8F51A5F9742F__INCLUDED_
#if _MSC_VER >= 1000
#pragma once
#endif // _MSC_VER >= 1000
// ViewPrintPreview.h : header file
//
#include "GridCtrl.h"
/////////////////////////////////////////////////////////////////////////////
// CViewPrintPreview view
class CViewPrintPreview : public CView
{
protected:
CViewPrintPreview(); // protected constructor used by dynamic creation
DECLARE_DYNCREATE(CViewPrintPreview)
// Attributes
public:
CGridCtrl *m_pCtrl;
CFrameWnd *m_pOldFrame;
// Operations
public:
virtual void OnFilePrintPreview();
// Overrides
// ClassWizard generated virtual function overrides
//{{AFX_VIRTUAL(CViewPrintPreview)
protected:
virtual void OnDraw(CDC* pDC); // overridden to draw this view
virtual void OnBeginPrinting(CDC* pDC, CPrintInfo* pInfo);
virtual void OnPrint(CDC* pDC, CPrintInfo* pInfo);
virtual void OnEndPrinting(CDC* pDC, CPrintInfo* pInfo);
virtual BOOL OnPreparePrinting(CPrintInfo* pInfo);
virtual void OnEndPrintPreview(CDC* pDC, CPrintInfo* pInfo, POINT point, CPreviewView* pView);
//}}AFX_VIRTUAL
// Implementation
protected:
virtual ~CViewPrintPreview();
#ifdef _DEBUG
virtual void AssertValid() const;
virtual void Dump(CDumpContext& dc) const;
#endif
// Generated message map functions
protected:
//{{AFX_MSG(CViewPrintPreview)
//}}AFX_MSG
DECLARE_MESSAGE_MAP()
};
/////////////////////////////////////////////////////////////////////////////
//{{AFX_INSERT_LOCATION}}
// Microsoft Developer Studio will insert additional declarations immediately before the previous line.
#endif // !defined(AFX_VIEWPRINTPREVIEW_H__137FC880_1607_11D3_9317_8F51A5F9742F__INCLUDED_)
<!-- end the block of source code -->
</FONT></TT></PRE>
<BR><BR><BR>
<h4>ViewPrintPreview implementation file:</h4>
<!-- start a block of source code -->
<PRE><TT><FONT COLOR="#990000">
// ViewPrintPreview.cpp : implementation file
//
#include "stdafx.h"
#include "ViewPrintPreview.h"
#ifdef _DEBUG
#define new DEBUG_NEW
#undef THIS_FILE
static char THIS_FILE[] = __FILE__;
#endif
/////////////////////////////////////////////////////////////////////////////
// CViewPrintPreview
IMPLEMENT_DYNCREATE(CViewPrintPreview, CView)
CViewPrintPreview::CViewPrintPreview()
{
m_pOldFrame=NULL;
}
CViewPrintPreview::~CViewPrintPreview()
{
}
BEGIN_MESSAGE_MAP(CViewPrintPreview, CView)
//{{AFX_MSG_MAP(CViewPrintPreview)
//}}AFX_MSG_MAP
END_MESSAGE_MAP()
/////////////////////////////////////////////////////////////////////////////
// CViewPrintPreview drawing
void CViewPrintPreview::OnDraw(CDC* pDC)
{
CDocument* pDoc = GetDocument();
// TODO: add draw code here
}
/////////////////////////////////////////////////////////////////////////////
// CViewPrintPreview diagnostics
#ifdef _DEBUG
void CViewPrintPreview::AssertValid() const
{
CView::AssertValid();
}
void CViewPrintPreview::Dump(CDumpContext& dc) const
{
CView::Dump(dc);
}
#endif //_DEBUG
/////////////////////////////////////////////////////////////////////////////
// CViewPrintPreview message handlers
void CViewPrintPreview::OnFilePrintPreview()
{
CView::OnFilePrintPreview();
}
BOOL CViewPrintPreview::OnPreparePrinting(CPrintInfo* pInfo)
{
return DoPreparePrinting(pInfo);
}
void CViewPrintPreview::OnBeginPrinting(CDC* pDC, CPrintInfo* pInfo)
{
m_pCtrl->OnBeginPrinting(pDC, pInfo);
}
void CViewPrintPreview::OnPrint(CDC* pDC, CPrintInfo* pInfo)
{
m_pCtrl->OnPrint(pDC, pInfo);
}
void CViewPrintPreview::OnEndPrinting(CDC* pDC, CPrintInfo* pInfo)
{
m_pCtrl->OnEndPrinting(pDC, pInfo);
}
void CViewPrintPreview::OnEndPrintPreview(CDC* pDC, CPrintInfo* pInfo, POINT point, CPreviewView* pView)
{
CView::OnEndPrintPreview(pDC, pInfo, point, pView);
// Show the original frame
m_pOldFrame->ShowWindow(SW_SHOW);
// Restore main frame pointer
AfxGetApp()->m_pMainWnd=m_pOldFrame;
m_pCtrl->m_bPrintPreview=FALSE;
// Kill parent frame and itself
GetParentFrame()->DestroyWindow();
}
<!-- end the block of source code -->
</FONT></TT></PRE>
<!-- demo project -->
<p><A HREF="http://www.geocities.com/SiliconValley/Lakes/6165/preview.zip">Download demo project - 247 KB</A>
<p>Date Posted: May 31, 1999
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