解決方案

1、使用 virtual BOOL PreTranslateMessage(MSG* pMsg);截獲WM_PAINT訊息，並推送WM_PAINT訊息

2、在OnPaint事件中新增背景圖片或顏色

demo：

MainFrame.h
	afx_msg void OnPaint();
	virtual BOOL PreTranslateMessage(MSG* pMsg);

MainFrame.cpp
BEGIN_MESSAGE_MAP(CMainFrame, CBCGPMDIFrameWnd)
	ON_WM_PAINT()
END_MESSAGE_MAP()
BOOL CMainFrame::PreTranslateMessage(MSG* pMsg)
{
	// TODO: 在此新增專用程式碼和/或呼叫基類
	if(pMsg->hwnd==m_hWndMDIClient && pMsg->message==WM_PAINT)
		PostMessage(WM_PAINT); 
	return CBCGPMDIFrameWnd::PreTranslateMessage(pMsg);
}

void CMainFrame::OnPaint()
{
//	CPaintDC dc(this); // device context for painting
	CDC dc,memdc;
	dc.m_hDC=::GetDC(this->m_hWndMDIClient);
	CRect rect;
	CBitmap bitmap;
	BITMAP szbitmap;
	bitmap.LoadBitmap(IDB_BMP_START);
	bitmap.GetObject(sizeof(BITMAP),&szbitmap);

	CSize size(szbitmap.bmWidth,szbitmap.bmHeight);
	memdc.CreateCompatibleDC(&dc);
	CBitmap *oldbitmap=memdc.SelectObject(&bitmap);
	GetClientRect(&rect);
	StretchBlt(dc.m_hDC,0,0,rect.Width(),rect.Height(),memdc.m_hDC,0,0,size.cx,size.cy,SRCCOPY);
	memdc.SelectObject(oldbitmap);
	memdc.DeleteDC();
	dc.DeleteDC();
	CBCGPMDIFrameWnd::OnPaint();
}
 

resource.h
#define IDB_BMP_START                   147

*.rc
/////////////////////////////////////////////////////////////////////////////
//
// Bitmap
//
IDB_BMP_START           BITMAP                  "res\\圖片5.BMP"