Rectangle not showing on OnPaint MFC - c++

Question

I have a dialog based application written in c++ and MFC. The dialog has a CStatic picture control. I am drawing a BITMAP in the OnPaint() function of the PictureCtrl. The relevant code is as follows:
void PictureCtrl::OnPaint()
{
CDC* pDC = this->GetDC();
pDC->SelectStockObject(PS_SOLID);
pDC->Rectangle(CRect(0, 0, 400, 400));
ReleaseDC(pDC);
CStatic::OnPaint();
}
When the application runs, the rectangle is drawn right on the top-left corner of the dialog, and not the picture control.
Secondly, if I minimize and maximize the dialog window, the image shows up, but the rectangle doesn't.
However, if I hover the mouse in the windows taskbar and a tooltip appears on the icon of the dialog application, the rectangle shows up.
I want to show the rectangle over the image no matter what the user does to the window (minimize, maximize, move, etc.).

Answer 1

CStatic::OnPaint handles BeginPaint/EndPaint (main WinAPI functions) in response to WM_PAINT message. Therefore it should be called first. Moreover, you can use CClientDC which has automatic clean up:
void PictureCtrl::OnPaint()
{
CStatic::OnPaint();
CClientDC dc(this); //<- uses GetDC
dc.SelectStockObject(BLACK_PEN);
dc.Rectangle(CRect(0, 0, 400, 400));
} //<- ReleaseDC is automatically called
Better yet, use CPaintDC directly in response to WM_PAINT message:
void PictureCtrl::OnPaint()
{
CPaintDC dc(this); //<- calls `BeginPaint`
dc.SelectStockObject(BLACK_PEN);
dc.Rectangle(CRect(0, 0, 400, 400));
} //<- EndPaint is automatically called
Unrelated, use BLACK_PEN as parameter for SelectStockObject. Use PS_SOLID as parameter for CPen:
CPen pen(PS_SOLID, 1, RGB(0,0,0));