memdc.h

WinCE 下实现Listctrl自画

#ifndef _MEMDC_H_
#define _MEMDC_H_


class CMemDC : public CDC
 {

private:	
	CBitmap		m_bitmap;		// Offscreen bitmap
	CBitmap*	m_oldBitmap;	// bitmap originally found in CMemDC
	CDC*		m_pDC;			// Saves CDC passed in constructor
	CRect		m_rect;			// Rectangle of drawing area.
	BOOL		m_bMemDC;		// TRUE if CDC really is a Memory DC.

public:	
	CMemDC(CDC* pDC, const CRect* pRect = NULL, BOOL bBg = FALSE) : CDC()
	{
		ASSERT(pDC != NULL); 

		// Some initialization
		m_pDC = pDC;
		m_oldBitmap = NULL;
		m_bMemDC = !pDC->IsPrinting();

		// Get the rectangle to draw
		if (pRect == NULL) 
		{
			pDC->GetClipBox(&m_rect);
		} 
		else
		{
			m_rect = *pRect;
		}

		if (m_bMemDC) 
		{
			// Create a Memory DC
			CreateCompatibleDC(pDC);
			pDC->LPtoDP(&m_rect);
			m_bitmap.CreateCompatibleBitmap(pDC, m_rect.Width(), m_rect.Height());
			m_oldBitmap = SelectObject(&m_bitmap);
			pDC->DPtoLP(&m_rect);

		} 
		else 
		{
			// Make a copy of the relevent parts of the current DC for printing
			m_bPrinting = pDC->m_bPrinting;
			m_hDC       = pDC->m_hDC;
			m_hAttribDC = pDC->m_hAttribDC;
		}

		// Fill background 
		if( bBg )
			BitBlt(m_rect.left, m_rect.top, m_rect.Width(), m_rect.Height(),
				m_pDC, m_rect.left, m_rect.top, SRCCOPY);
		else
			FillSolidRect(m_rect, pDC->GetBkColor());
	}
	
	~CMemDC()	
	{		
		if (m_bMemDC)
		{
			// Copy the offscreen bitmap onto the screen.
			m_pDC->BitBlt(m_rect.left, m_rect.top, m_rect.Width(), m_rect.Height(),
				this, m_rect.left, m_rect.top, SRCCOPY);			
			
			//Swap back the original bitmap.
			SelectObject(m_oldBitmap);		
		} 
		else 
		{
			// All we need to do is replace the DC with an illegal value,
			// this keeps us from accidently deleting the handles associated with
			// the CDC that was passed to the constructor.			
			m_hDC = m_hAttribDC = NULL;
		}	
	}
		
	CMemDC* operator->() 
	{
		return this;
	}	

	operator CMemDC*() 
	{
		return this;
	}
};

#endif