[RESOLVED] Print preview ASSERT problem

[Buzzyous]

Hi to all

Maybe this is a stupid question, but I looked around in internet and searched this forum for this problem. I didn't found anything free and useful

The fact is, I have an application SDI with a view that produces a custom report. When I go for print preview, I got an ASSERT from line 562 in afxwin1.inl. The code that Asserts is

_AFXWIN_INLINE HGDIOBJ CDC::SelectObject(HGDIOBJ hObject) // Safe for NULL handles
	{ ASSERT(m_hDC == m_hAttribDC); // ASSERT a simple CDC object
		return (hObject != NULL) ? ::SelectObject(m_hDC, hObject) : NULL; }

The app continues working after hitting the ignore button, but I think I shoul solve this fact; i suspect doing something wrong.


Thanks in advance for the help

[JohnCz]

It tells you that your CDC object does not have windows device context attached to it.
I do not know how you instantiate CDC object but both: m_hAttribDC and m_hDC are initiated to the same value (0) when object is instantiated. You must have done something that changes one value. This function is safe if both values are NULL.
By the way to construct a valid object, you should somehow attach windows device context by either using Attach or obtaining device context from the window, or use Createxxx to create device context.

[Buzzyous]

I did nothing, just used the native OnPrint, importing a CRect with the size given by CPrintInfo struct in onDraw if (pDC->IsPrinting()).

it is the first time I need to print something in visual c++, I thought OnPreparePrinting() and OnPrepareDC() initializes a printing device context and passes it to OnDraw when printing.
Do I have to initialize something else regarding CDCs?

I used OnPrint with pInfo's m_nCurPage member to direct my printing. But Preview launches this ASSERT. Ignoring it, however, it works.

[JohnCz]

Indeed, OnPreparePrinting() and OnPrepareDC() should initialize device context properly.
If you do not need something fancy to print, OnDraw should handle printing as it were a screen.
It is really hard to guess what is going on, without seeing the code.
Woould it be possible to post zipped your (or sample) project that reproduces this error?

[Buzzyous]

I could post it, but there is nothing apart the standard functions:

void CFFView::OnInitialUpdate() 
{
	CScrollView::OnInitialUpdate();
	
	// TODO: Add your specialized code here and/or call the base class
	CSize sizeTotal;
	sizeTotal.cx = 0;
	sizeTotal.cy = 0;
	SetScrollSizes(MM_TEXT, sizeTotal);
}

BOOL CFFView::OnPreparePrinting(CPrintInfo* pInfo)
{
	// default preparation
	return DoPreparePrinting(pInfo);
}

void CFFView::OnBeginPrinting(CDC* /*pDC*/, CPrintInfo* /*pInfo*/)
{
	// TODO: add extra initialization before printing
}

void CFFView::OnEndPrinting(CDC* /*pDC*/, CPrintInfo* /*pInfo*/)
{
	// TODO: add cleanup after printing
}

void CFFView::OnPrint(CDC* pDC, CPrintInfo* pInfo) 
{
	// TODO: Add your specialized code here and/or call the base class
	if (pInfo) 
	{
		printArea = pInfo->m_rectDraw;
		curPrintPage = pInfo->m_nCurPage;
	}

//Page dependent print yet to implement

	CScrollView::OnPrint(pDC, pInfo);
}


BOOL CFFView::PreCreateWindow(CREATESTRUCT& cs)
{
	// TODO: Modify the Window class or styles here by modifying
	//  the CREATESTRUCT cs

	return CScrollView::PreCreateWindow(cs);
}

/////////////////////////////////////////////////////////////////////////////
// CYardManView drawing

void CFFView::OnDraw(CDC* pDC)
{
	CFont* oldfont = pDC->SelectObject(&reportFont);	
//reportFont is a class member of CFFView

	CString de; de.Format("pag %i", curPrintPage); AfxMessageBox(de);

	//I set some graphic params, like titles, margins and some other layout elements. 
	DefineReportParam(view); //view is also a class member of CFFView

	DrawReport(view, pDC); 
/*A function that draws a report. It uses CDC::TextOut(...), CDC::LineTo(...), CDC::MoveTo(...), CDC::FillSolidRect(...), CDC::GetTextExtent(...), CDC:SetTextAlign(...), CDC::SetTextColor(...), CDC::SeletcObject(...), CFont::DeleteObject(...), CFont::CreatePointFont */

	pDC->SelectObject(oldfont);
}

I did no custom CDC implementation, only passed the one given by OnDraw to a function specialized in drawing a custom report, which uses only standard graphics commands.

It could be the passing of the CDC* to a function outside OnDraw, or maybe some graphic command?

Still think I should post the full CFFView code or zip it? I will if you think it could help

[Buzzyous]

Ok, I found it.

The problem is about selecting a font created for the monitor device context into de printing device context.

Sorry for the bothering, this is solved now

Thank you, I should've debugged the program deeper before

I am sorry

[Buzzyous]

Actually, I realized something there is wrong

My OnPaint() function, at its start, already receives the pDC CDC with the two members m_hDC and m_hAttribDC different,without me having done anything, while when no printing is being performed, the CDC in OnDraw hav coherent members

The strange thing number 1 is that these two members are different in the printing device context that the framework itself creates.
Also, I examined a brand new MFC SDI document, and the plain override of OnPrint exhibits exactly the same problem, different handler pointers for the printing device context, so this fact is frameword-dependent, not derived from my code.

The second strange thing, strangest, is that I use SelectObject twice before the one that produces the ASSERT, which is produced only when I select a font, class member of my CScrollView derived class, initialized and created in its constructor.

Any idea on why this happens?

PS don't know how to un-Resolve the thread

[JohnCz]

Can you compress and post your project?
I was trying to follow your instructions but I am not able to duplicate the problem.