(continued)

Thanks to Chris Maunder for introducing the printing method in Printing without the Document/View framework. 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 CViewOnFilePrintPreview( ) and CViewDoPrintPreview. They are undocumented, the source code can be found from VC\mfc\src\Viewprev.cpp. The implementation relies on CView and CFrameWnd framework extensively.

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 Chris Maunder's CGridCtrl control from MFC Grid control (derived from CWnd) 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. )

How to use

// In your header file /////////////
private
    CSingleDocTemplate* m_pTemplate;
public
    BOOL m_bPrintPreview;
    void PrintPreview();
////////////////////////////////////

// In your class constructor ///////
#include "ViewPrintPreview.h"

CGridCtrlCGridCtrl(...)
{
    // Add initialization
    m_pTemplate=NULL;
    m_bPrintPreview=FALSE;
}
////////////////////////////////////

// In your class ///////////////////
void CGridCtrlPrintPreview()
{
    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();
}

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.

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.

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

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 CDialogContinueModal();
}

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.

Finally, I wish you happy previewing! :)

ViewPrintPreview header file

#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_)

ViewPrintPreview implementation file

// 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()
{
    CViewOnFilePrintPreview();
}

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();
}

Downloads

Download demo project - 100 Kb

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