Thread: Problem with create style of CChildFrame

I am creating MDI project using extended classes : CMDIFrameWndExCWinAppExCMDIChildWndExMy view class is derived from CScrollView.Code is working fine if I don't apply any style to Child window in PreCreateWindow. But when i apply style with visibility true then some debug assertion comes.On debugging further i came to know that asertion comes in below block while redrawing window.

Code:

void CMFCBaseTabCtrl::SetLocation(Location location)
{
ASSERT_VALID(this);
m_location = location;
RecalcLayout();
if (GetSafeHwnd() != NULL)
{
GetParent()->RedrawWindow(NULL, NULL, RDW_INVALIDATE | RDW_UPDATENOW | RDW_ERASE | RDW_ALLCHILDREN);
}
}

other thing which i noticed is that when child window is created with style with WS_VISIBLE then Ondraw() of view class is called before OnInitialUpdate()

My code and logic was working fine without using extended classes so i don't want to change it as it would be a lot of re-work. So can anybody guide me what to do ?

To reproduce the assertion:

Just create a new project and inherit the view class with CSrcollView. Extend your classes with
CMDIFrameWndEx, CMDIChildWndEx, CWinAppEx
repectively. Set scroll size in oninitialupdate of view class. Now run the progam without opening any window on startup. Open the document. New tab is created. Its working fine. Now add following lines in
CChildFrame::PreCreateWindow(CREATESTRUCT& cs)

Code:

cs.style = WS_CHILD | WS_VISIBLE | WS_OVERLAPPED | WS_CAPTION | WS_SYSMENU | FWS_ADDTOTITLE | WS_EX_CLIENTEDGE | WS_MAXIMIZEBOX | WS_MAXIMIZE;

Now u will get assertion at:

Code:

 
void CScrollView::OnPrepareDC(CDC* pDC, CPrintInfo* pInfo)
{
...
#ifdef
_DEBUG 
if (m_nMapMode == MM_NONE){ 
TRACE(traceAppMsg, 0,
"Error: must call SetScrollSizes() or SetScaleToFitSize()"); 
TRACE(traceAppMsg, 0)
"\tbefore painting scroll view.\n"); 
ASSERT(FALSE);
return;
}

If i remove WS_VISIBLE style, then there is no assertion. I don't know the reason.
To resolve this i just added

Code:

 m_nMapMode = MM_TEXT;

in constructor of view class.
So it is working fine. But still i don't understand why OnDraw is called before OnInitialUpdate() in this case as this is totally shaking my logic.

Now my actual problem starts. I have to call a function of a class in OnInitialUpdate. In that function I have to point view class object. i am getting view class like

(MyViewClass*)((CMDIFrameWnd*)AfxGetMainWnd())->MDIGetActive()->GetActiveView())


on further modularising above line i came to know that MDIGetActive is returning null.

now can anyone help me out.