OnDraw not getting called - c++

Question

I'm trying to display an image in CScrollView-derived class:
C++ CScrollView, how to scroll an image?
So I want to override OnDraw, to move the code from OnPaint to OnDraw. But I can't. Every time I call Invalidate() only OnPaint is getting called.
void CCardioAppView::OnDraw(CDC* pDC)
{
}
void CCardioAppView::OnPaint()
{
if (theApp.ImageFolderPath == _T("")) return;
//---------------------метод № 2 с CPictureHolder-------------------------------
CPaintDC dc(this);
CBitmap bmp;
BITMAP b;
HBITMAP hbitmap;
CRect rect;
auto bmp_iter = theApp.FullBmpMap.find(m_iCurrentImage);
if (bmp_iter == theApp.FullBmpMap.end()) return;
hbitmap = bmp_iter->second;
bmp.Attach((*bmp_iter).second);
bmp.GetObject(sizeof(BITMAP), &b);
GetClientRect(&rect);
scaleRect = rect;
OriginalWidth = b.bmWidth;
OriginalHeight = b.bmHeight;
if (rect.Height() <= b.bmHeight)
scaleRect.right = rect.left + ((b.bmWidth*rect.Height()) / b.bmHeight);
else if (rect.Height() > b.bmHeight)
{
scaleRect.right = b.bmWidth;
scaleRect.bottom = b.bmHeight;
}
scaleRect.right = scaleRect.right + scale_koef_g;
scaleRect.bottom = scaleRect.bottom + scale_koef_v;
pic.CreateFromBitmap(hbitmap);
pic.Render(&dc, scaleRect, rect);
(*bmp_iter).second.Detach();
(*bmp_iter).second.Attach(bmp);
bmp.Detach();
int isclWidth = scaleRect.Width();
int isclHeight = scaleRect.Height();
int irHeight = rect.Height();
int irWidth = rect.Width();
if ((isclWidth> irWidth)||(isclHeight > irHeight))
{
SetScrollSizes(MM_TEXT, CSize(isclWidth, isclHeight));
}
else SetScrollSizes(MM_TEXT, CSize(irWidth, irHeight));
}

Answer 1

Of course it doesn't call OnDraw(). When you call Invalidate() it ends up with a WM_PAINT message for the CView derived class. The default implementation of CView::OnPaint() gets a paint DC and then it later calls CView::OnDraw(). You are overriding OnPaint() and you never call OnDraw() in your OnPaint() handler.
You can move some of your OnPaint() code into OnDraw() except for obvious stuff like CPaintDC dc(this);
After that you can delete your OnPaint() declaration and implementation. Then, delete your ON_WM_PAINT() message map entry. I can't vouch either way for your drawing code.