Redraw shapes in MFC - c++

Question

I'm trying to develop a painter app using MFC with C++.
So I set up a view in which I do the actual painting. However, when I open the color button I get "leftovers" of the menu on my canvas view.. I have no idea how to erase them.. I tried using SaveDC and RestoreDC to restore it to the previous state but no luck there. As I understand it is meant to restore properties of the device context such as pen & brush but it has no use for me...
I also need this feature so when I put up a rectangle, I could present a preview for it, but the "previews` are again presented like leftovers.
My view's OnEraseBkgbd;
BOOL CanvasView::OnEraseBkgnd(CDC* pDC)
{
if (!isBackgroundInit)
{
CRect rect;
GetClientRect(&rect);
CBrush myBrush(RGB(255, 255, 255)); // dialog background color
CBrush* pOld = pDC->SelectObject(&myBrush);
BOOL bRes = pDC->PatBlt(0, 0, rect.Width(), rect.Height(), PATCOPY);
pDC->SelectObject(pOld); // restore old brush
isBackgroundInit = true;
return bRes;
}
return 0;
}
My OnPaint:
void CanvasView::OnPaint()
{
CDialogEx::OnPaint();
//UpdateData(true);
CRect rect;
GetClientRect(&rect);
if (dc == nullptr)
{
dc = new CClientDC(this);
//dc->CreateCompatibleDC(dc);
HDC hdc = CreateCompatibleDC(*dc);
this->hdc = &hdc;
} else
{
BitBlt(*dc, 0, 0, (int)rect.Width(), (int)rect.Height(), *hdc, 0, 0, SRCCOPY);
}
}
How it looked at first:
How it looks when opening a color button:
How it looks after closing the color button menu(leftovers marked with red arrows):
When trying to put up a rectangle:
Any idea how to fix this and really restore drawing?

Answer 1

I am not sure I understand what you are trying to do.
CView has a virtual method called OnDraw. This is the method you must override:
void CMyView::OnDraw(CDC* pDC)
{
CMyDoc* pDoc = GetDocument();
ASSERT_VALID(pDoc);
if (!pDoc)
return;
// first erase the entire client rectangle
CRect cr;
GetClientRect( &cr );
pDC->FillSolidRect( cr, RGB( 255, 255, 255 ) );
// your actual drawing goes here
pDC->Rectangle( 0, 0, 100, 100 );
}
You will also have to write OnEraseBkgnd:
BOOL CMyView::OnEraseBkgnd( CDC* /*pDC*/ )
{
return TRUE; // we fill the client rectangle in OnDraw
}
Also, it looks like you are trying to implement an ad-hoc memory DC. There is already one: CMemDC.