又是断言失败

mengde007 2010-08-31 10:23:49



//各位友人，我在一个函数里面如果触发了一次wm_drawitem消息的时候，下列断言不会有任何异常，如果在那个函数里面2次触发wm_drawitem消息的时候，为什么就会引发断言失败呢；很奇怪啊；望解答。

//从CBitmapButton继承过来的类

void CMybutton::DrawItem(LPDRAWITEMSTRUCT lpDIS)

{

	ASSERT(lpDIS != NULL);

	// must have at least the first bitmap loaded before calling DrawItem

	ASSERT(m_bitmap.m_hObject != NULL);     // 就是这儿，断言失败了



	// use the main bitmap for up, the selected bitmap for down

	CBitmap* pBitmap = &m_bitmap;

	UINT state = lpDIS->itemState;

	if ((state & ODS_SELECTED) && m_bitmapSel.m_hObject != NULL)

		pBitmap = &m_bitmapSel;

	else if ((state & ODS_FOCUS) && m_bitmapFocus.m_hObject != NULL)

		pBitmap = &m_bitmapFocus;   // third image for focused

	else if ((state & ODS_DISABLED) && m_bitmapDisabled.m_hObject != NULL)

		pBitmap = &m_bitmapDisabled;   // last image for disabled



	// draw the whole button

	CDC* pDC = CDC::FromHandle(lpDIS->hDC);

	

	

	CDC memDC;

	memDC.CreateCompatibleDC(pDC);

	CBitmap* pOld = memDC.SelectObject(pBitmap);

	if (pOld == NULL)

		return;     // destructors will clean up



	CRect rect;

	rect.CopyRect(&lpDIS->rcItem);

/*

	pDC->BitBlt(rect.left, rect.top, rect.Width(), rect.Height(),

		&memDC, 0, 0, SRCCOPY);

*/

	 BITMAP bits;

         pBitmap->GetObject(sizeof(BITMAP),&bits);

         pDC->StretchBlt(rect.left,rect.top,rect.Width(),rect.Height(),

            &memDC,0,0,bits.bmWidth, bits.bmHeight, SRCCOPY);

								

		

	pDC->SetBkMode(TRANSPARENT);



	memDC.SelectObject(pOld);

}