Can someone explain the problem with this?

I'm pulling my hair out at tho moment over run time errors, I seem to get another exception / debug assert error for every other line I write.

One that's causing me confusion is:

Code:

BOOL CMyPropPage::OnSetActive() 
{
	CMyFormDoc* pDoc = (CMyFormDoc*)GetDocument();

	return CPropertyPage::OnSetActive();
}

The reported error is on line 45 of objcore.cpp. Can anyone solve this and give me some tips on why these things occur?

-edit-
I'm using MFC and VC6 with an appwizard generated MDI using doc/view.

>Can anyone solve this and give me some
>tips on why these things occur?

Difficult. Have you tried using the debugger ? And can you post your whole code at least for the part where the error occurs ? Because the function 'as is' makes no sense but should not crash.

If you get debug assertions, it should tell you where it fails and what it checks. Jump into the line and see what it checks when the assertion fails.

I've got a full function but in trying to find the source of the error I had commented everything out except that line, my full function is

Code:

/////////////////////////////////////////////////////////////////////////////
// CMyPropPage message handlers

CTykeDoc* CMyPropPage::GetDocument() // non-debug version is inline
{
	ASSERT(m_pDocument->IsKindOf(RUNTIME_CLASS(CTykeDoc)));
	return (CTykeDoc*)m_pDocument;
}



BOOL CMyPropPage::OnSetActive() 
{
	CTykeDoc* pDoc = (CTykeDoc*)m_pDocument->IsKindOf(RUNTIME_CLASS(CTykeDoc));//GetDocument();


	


	//** get pointers to the recordsets
	m_pMyDaoRecordSet      = pDoc->m_pMyDaoRecordSet;


	UINT nCount =PopulateCustomerList();
	
	if( nCount > 0 )
	{
		this->m_CustomerList.SetCurSel( 0 );
	}

	//CreateTabs();

	return CPropertyPage::OnSetActive();
}


UINT CMyPropPage::PopulateCustomerList()
{
	
	UINT nCount = 0;
	ASSERT( m_pMyDaoRecordSet->IsOpen() == TRUE);
		

	try{


	if( !m_pMyDaoRecordSet->IsBOF() )
	{
		m_CustomerList.ResetContent();
		
		m_pMyDaoRecordSet->MoveFirst();

		while( !m_pMyDaoRecordSet->IsEOF() )
		{
			m_CustomerList.AddString( m_pMyDaoRecordSet->m_CCompany_Name );
			m_pMyDaoRecordSet->MoveNext();
			nCount++;
		}
	}

	}
	catch(CDaoException* e;)
	{
		e->ReportError();
		e->Delete();
	}

	return nCount;
}

I can send the full thing as an attachment if needed but it's too much to post here.

Here's the line it fails on in objcore:

Code:

BOOL CObject::IsKindOf(const CRuntimeClass* pClass) const
{
	ASSERT(this != NULL);
	// it better be in valid memory, at least for CObject size
	ASSERT(AfxIsValidAddress(this, sizeof(CObject)));

	// simple SI case
	CRuntimeClass* pClassThis = GetRuntimeClass();
	return pClassThis->IsDerivedFrom(pClass); // POINTS TO HERE
}

A lot of the code is adapted from zMan's demo, just so he doesnt think I'm taking credit, the functions in his demo are used inside a CFormView class, instead of CPropertyPage and he uses OnInitUpdate where I have used OnSetActive.

First obvious iregularity: IsKindOf returns a BOOL. You cast that into a pointer to an object. This will always yield a null pointer or an invalid pointer as result.

Assuming this is for debugging and you used GetDocument normally, make sure your own TykeDoc class implements all those macros neccessary for the RUNTIME_CLASS macros used. Look in your help for DECLARE_ and IMPLEMENT_ macros, there are three types.

If this is a Debug Assertion, find the line where it asserts. It will tell you what happened. If it is a crash, find the line where it crashes, it will help as well. Trace the stackwalk to your last own line of code and see what might be wrong with that.


Sidenote:

I never used Doc/View with a CDialog derived class. I'm not sure you can do it this way.