为什么加载的位图动画不显示呢？

class MemDC :
    public CDC
{
    CSize m_size;
public:
    MemDC(void);
   
    ~MemDC(void);
   
    //加载进程内位图的构造函数
    MemDC(UINT nBitmap,CDC* pDC=NULL)
    {
        LoadBitmap( nBitmap,pDC);
    }
    //加载进程外位图的构造函数
    MemDC(LPCWSTR szFile, CDC* pDC=NULL)
    {
        LoadBitmap( szFile,  pDC);
    }
    //创建空白位图的构造函数
    MemDC(int cx, int cy,CDC* pDC=NULL)
    {
        Create( cx, cy, pDC);
    }
    int GetWidth()
    {return m_size.cx;}
    int GetHeight()
    {return m_size.cy;}
    BOOL DeleteDC()
    {
        if (!GetSafeHdc())
            return FALSE;
        CBitmap *pBitmap=GetCurrentBitmap();
        if(pBitmap)
            pBitmap->DeleteObject();
        return CDC::DeleteDC();
    }
    //创建空白位图
    BOOL Create(int cx, int cy,CDC* pDC=NULL)
    {
        CBitmap bmp;
        if (!bmp.CreateCompatibleBitmap(pDC,cx,cy))
            return FALSE;
        m_size.cx=cx;
        m_size.cy=cy;
        CreateCompatibleDC(pDC);
        SelectObject(&bmp);
        return TRUE;
    }
    //进程内资源加载

    BOOL  LoadBitmap(UINT nBitmap,CDC* pDC=NULL)
    {
        CBitmap bmp;
        if (!bmp.LoadBitmap(nBitmap))
            return FALSE;
        BITMAP bm;
        bmp.GetBitmap(&bm);
        m_size.cx=bm.bmWidth;
        m_size.cy=bm.bmHeight;
        CreateCompatibleDC(pDC);
        SelectObject(&bmp);
        return TRUE;
    }
    //进程外位图图片加载
    BOOL LoadBitmap(LPCWSTR szFile, CDC* pDC=NULL)
    {
        HBITMAP hBitmap = (HBITMAP)LoadImage(NULL,szFile,IMAGE_BITMAP,
            0,0,LR_LOADFROMFILE);
        if (!hBitmap)
            return FALSE;
        BITMAP bm;
        GetObject(hBitmap,sizeof(bm),&bm);
        m_size.cx=bm.bmWidth;
        m_size.cy=bm.bmHeight;
        CreateCompatibleDC(pDC);
        SelectObject(hBitmap);
        return TRUE;

    }
};